add safer, more versatile version of rapidhash for any array and for any iterable

Tested that it gives the same answer on random data, and that
performance is equivalent (with LLVM 20 on AArch64).

```
julia> using BenchmarkTools, Random; for n = 0:67:1000
         a = (i % UInt8 for i in 1:n)
         b = collect(a)
         ## Same results for [] and String
         # b = codeunits(randstring(n))
         # a = Base.Generator(identity, b)
         @Btime Base.hash_bytes($a, Base.HASH_SEED, Base.HASH_SECRET)
         @Btime Base.hash_bytes($b, Base.HASH_SEED, Base.HASH_SECRET)
         @Btime Base.hash_bytes(pointer($b), length($b), Base.HASH_SEED, Base.HASH_SECRET)
         println()
       end
  5.666 ns (0 allocations: 0 bytes) # iterator
  3.625 ns (0 allocations: 0 bytes) # array
  3.625 ns (0 allocations: 0 bytes) # pointer

  20.269 ns (0 allocations: 0 bytes)
  5.375 ns (0 allocations: 0 bytes)
  5.083 ns (0 allocations: 0 bytes)

  35.624 ns (0 allocations: 0 bytes)
  6.250 ns (0 allocations: 0 bytes)
  6.208 ns (0 allocations: 0 bytes)

  50.954 ns (0 allocations: 0 bytes)
  7.625 ns (0 allocations: 0 bytes)
  7.334 ns (0 allocations: 0 bytes)

  66.496 ns (0 allocations: 0 bytes)
  9.083 ns (0 allocations: 0 bytes)
  8.875 ns (0 allocations: 0 bytes)

  82.299 ns (0 allocations: 0 bytes)
  10.719 ns (0 allocations: 0 bytes)
  10.511 ns (0 allocations: 0 bytes)

  98.346 ns (0 allocations: 0 bytes)
  12.888 ns (0 allocations: 0 bytes)
  12.513 ns (0 allocations: 0 bytes)
```

Author: vtjnash

base/hashing.jl

@@ -344,6 +344,293 @@ load_le(::Type{T}, ptr::Ptr{UInt8}, i) where {T <: Union{UInt32, UInt64}} =
     return hash_mix(a ⊻ secret[4], b ⊻ secret[2] ⊻ i)
 end
 
+@inline function load_le_array(::Type{UInt64}, arr::AbstractArray{UInt8}, idx)
+    # n.b. for whatever reason, writing this as a loop ensures LLVM
+    # optimizations (particular SROA) don't make a disaster of this code
+    # early on so it can actually emit the optimal result
+    result = zero(UInt64)
+    for i in 0:7
+        byte = @inbounds arr[idx + i]
+        result |= UInt64(byte) << (8 * i)
+    end
+    return result
+end
+
+@inline function load_le_array(::Type{UInt32}, arr::AbstractArray{UInt8}, idx)
+    result = zero(UInt32)
+    for i in 0:3
+        byte = @inbounds arr[idx + i]
+        result |= UInt32(byte) << (8 * i)
+    end
+    return result
+end
+
+@assume_effects :terminates_globally function hash_bytes(
+        arr::AbstractArray{UInt8},
+        seed::UInt64,
+        secret::NTuple{4, UInt64}
+    )
+    # Adapted with gratitude from [rapidhash](https://github.com/Nicoshev/rapidhash)
+    n = length(arr)
+    buflen = UInt64(n)
+    seed = seed ⊻ hash_mix(seed ⊻ secret[3], secret[2])
+    firstidx = firstindex(arr)
+
+    a = zero(UInt64)
+    b = zero(UInt64)
+    i = buflen
+
+    if buflen ≤ 16
+        if buflen ≥ 4
+            seed ⊻= buflen
+            if buflen ≥ 8
+                a = load_le_array(UInt64, arr, firstidx)
+                b = load_le_array(UInt64, arr, firstidx + n - 8)
+            else
+                a = UInt64(load_le_array(UInt32, arr, firstidx))
+                b = UInt64(load_le_array(UInt32, arr, firstidx + n - 4))
+            end
+        elseif buflen > 0
+            a = (UInt64(@inbounds arr[firstidx]) << 45) | UInt64(@inbounds arr[firstidx + n - 1])
+            b = UInt64(@inbounds arr[firstidx + div(n, 2)])
+        end
+    else
+        pos = 0
+        if i > 48
+            see1 = seed
+            see2 = seed
+            while i > 48
+                seed = hash_mix(
+                    load_le_array(UInt64, arr, firstidx + pos) ⊻ secret[1],
+                    load_le_array(UInt64, arr, firstidx + pos + 8) ⊻ seed
+                )
+                see1 = hash_mix(
+                    load_le_array(UInt64, arr, firstidx + pos + 16) ⊻ secret[2],
+                    load_le_array(UInt64, arr, firstidx + pos + 24) ⊻ see1
+                )
+                see2 = hash_mix(
+                    load_le_array(UInt64, arr, firstidx + pos + 32) ⊻ secret[3],
+                    load_le_array(UInt64, arr, firstidx + pos + 40) ⊻ see2
+                )
+                pos += 48
+                i -= 48
+            end
+            seed ⊻= see1
+            seed ⊻= see2
+        end
+        if i > 16
+            seed = hash_mix(
+                load_le_array(UInt64, arr, firstidx + pos) ⊻ secret[3],
+                load_le_array(UInt64, arr, firstidx + pos + 8) ⊻ seed
+            )
+            if i > 32
+                seed = hash_mix(
+                    load_le_array(UInt64, arr, firstidx + pos + 16) ⊻ secret[3],
+                    load_le_array(UInt64, arr, firstidx + pos + 24) ⊻ seed
+                )
+            end
+        end
+
+        a = load_le_array(UInt64, arr, firstidx + n - 16) ⊻ i
+        b = load_le_array(UInt64, arr, firstidx + n - 8)
+    end
+
+    a = a ⊻ secret[2]
+    b = b ⊻ seed
+    b, a = mul_parts(a, b)
+    return hash_mix(a ⊻ secret[4], b ⊻ secret[2] ⊻ i)
+end
+
+
+# Helper function to concatenate two UInt64 values with a byte shift
+# Returns the result of shifting 'low' right by 'shift_bytes' bytes and
+# filling the high bits with the low bits of 'high'
+@inline function concat_shift(low::UInt64, high::UInt64, shift_bytes::Int)
+    shift_bits = shift_bytes * 8
+    return (low >> shift_bits) | (high << (64 - shift_bits))
+end
+
+@eval @inline function read_uint64_from_uint8_iter(iter, state)
+    value = zero(UInt64)
+    bytes_read = 0
+    shift = 0
+
+    for _ in 1:8
+        next_result = iterate(iter, state)
+        next_result === nothing && break
+        byte, state = next_result
+        value |= UInt64(byte) << shift
+        shift += 8
+        bytes_read += 1
+        $(Expr(:loopinfo, (Symbol("llvm.loop.disable_nonforced"))))
+        $(Expr(:loopinfo, (Symbol("llvm.loop.vectorize.enable"), false)))
+    end
+
+    return value, state, bytes_read
+end
+
+@eval @inline function read_uint64_from_uint8_iter(iter)
+    next_result = iterate(iter)
+    next_result === nothing && return nothing
+
+    byte, state = next_result
+    value = UInt64(byte)
+    bytes_read = 1
+
+    # Loop for remaining bytes
+    for i in 2:8
+        next_result = iterate(iter, state)
+        next_result === nothing && break
+        byte, state = next_result
+        value |= UInt64(byte::UInt8) << ((i-1) * 8)
+        bytes_read += 1
+        $(Expr(:loopinfo, (Symbol("llvm.loop.disable_nonforced"))))
+        $(Expr(:loopinfo, (Symbol("llvm.loop.vectorize.enable"), false)))
+    end
+
+    return value, state, bytes_read
+end
+
+@assume_effects :terminates_globally function hash_bytes(
+        iter,
+        seed::UInt64,
+        secret::NTuple{4, UInt64}
+    )
+    seed = seed ⊻ hash_mix(seed ⊻ secret[3], secret[2])
+
+    a = zero(UInt64)
+    b = zero(UInt64)
+    buflen = zero(UInt64)
+
+    see1 = seed
+    see2 = seed
+    l0 = zero(UInt64)
+    l1 = zero(UInt64)
+    l2 = zero(UInt64)
+    l3 = zero(UInt64)
+    l4 = zero(UInt64)
+    l5 = zero(UInt64)
+    b0 = 0
+    b1 = 0
+    b2 = 0
+    b3 = 0
+    b4 = 0
+    b5 = 0
+    t0 = zero(UInt64)
+    t1 = zero(UInt64)
+
+    # Handle first iteration separately
+    read = read_uint64_from_uint8_iter(iter)
+    if read !== nothing
+        l0, state, b0 = read
+        # Repeat hashing chunks until a short read
+        while true
+            l1, state, b1 = read_uint64_from_uint8_iter(iter, state)
+            if b1 == 8
+                l2, state, b2 = read_uint64_from_uint8_iter(iter, state)
+                if b2 == 8
+                    l3, state, b3 = read_uint64_from_uint8_iter(iter, state)
+                    if b3 == 8
+                        l4, state, b4 = read_uint64_from_uint8_iter(iter, state)
+                        if b4 == 8
+                            l5, state, b5 = read_uint64_from_uint8_iter(iter, state)
+                            if b5 == 8
+                                # Read start of next chunk
+                                read = read_uint64_from_uint8_iter(iter, state)
+                                if read[3] == 0
+                                    # Read exactly 48 bytes
+                                    t0 = l4
+                                    t1 = l5
+                                    break
+                                else
+                                    # Read more than 48 bytes - process and continue to next chunk
+                                    seed = hash_mix(l0 ⊻ secret[1], l1 ⊻ seed)
+                                    see1 = hash_mix(l2 ⊻ secret[2], l3 ⊻ see1)
+                                    see2 = hash_mix(l4 ⊻ secret[3], l5 ⊻ see2)
+                                    buflen += 48
+                                    l0, state, b0 = read
+                                    b1 = 0
+                                    b2 = 0
+                                    b3 = 0
+                                    b4 = 0
+                                    b5 = 0
+                                    if b0 != 8
+                                        t0 = concat_shift(l4, l5, b0)
+                                        t1 = concat_shift(l5, l0, b0)
+                                        break
+                                    end
+                                end
+                            else
+                                # Extract final 16 bytes at the first short read
+                                t0 = concat_shift(l3, l4, b5)
+                                t1 = concat_shift(l4, l5, b5)
+                                break
+                            end
+                        else
+                            t0 = concat_shift(l2, l3, b4)
+                            t1 = concat_shift(l3, l4, b4)
+                            break
+                        end
+                    else
+                        t0 = concat_shift(l1, l2, b3)
+                        t1 = concat_shift(l2, l3, b3)
+                        break
+                    end
+                else
+                    t0 = concat_shift(l0, l1, b2)
+                    t1 = concat_shift(l1, l2, b2)
+                    break
+                end
+            else
+                t0 = concat_shift(l5, l0, b1)
+                t1 = concat_shift(l0, l1, b1)
+                break
+            end
+        end
+    end
+
+    # Partial chunk, handle based on size
+    bytes_chunk = b0 + b1 + b2 + b3 + b4 + b5
+    if buflen > 0
+        # Finalize last full chunk
+        seed ⊻= see1
+        seed ⊻= see2
+    end
+    buflen += bytes_chunk
+    if buflen ≤ 16
+        if buflen ≥ 4
+            seed ⊻= buflen
+            if buflen ≥ 8
+                a = l0
+                b = t1
+            else
+                a = UInt64(l0 % UInt32)
+                b = UInt64((l0 >>> (8 * (bytes_chunk - 4))) % UInt32)
+            end
+        elseif buflen > 0
+            b0 = l0 % UInt8
+            b1 = (l0 >>> (8 * div(buflen, 2))) % UInt8
+            b2 = (l0 >>> (8 * (buflen - 1))) % UInt8
+            a = (UInt64(b0) << 45) | UInt64(b2)
+            b = UInt64(b1)
+        end
+    else
+        if bytes_chunk > 16
+            seed = hash_mix(l0 ⊻ secret[3], l1 ⊻ seed)
+            if bytes_chunk > 32
+                seed = hash_mix(l2 ⊻ secret[3], l3 ⊻ seed)
+            end
+        end
+        a = t0 ⊻ bytes_chunk
+        b = t1
+    end
+
+    a = a ⊻ secret[2]
+    b = b ⊻ seed
+    b, a = mul_parts(a, b)
+    return hash_mix(a ⊻ secret[4], b ⊻ secret[2] ⊻ bytes_chunk)
+end
+
 @assume_effects :total hash(data::String, h::UInt) =
     GC.@preserve data hash_bytes(pointer(data), sizeof(data), UInt64(h), HASH_SECRET) % UInt