Fix type inference and performance problems of munge_data

[devmotion]

The PR fixes a few issues related to #389.

On the master branch:

julia> using DataInterpolations, JET, Chairmarks, Random, Test

julia> @inferred(DataInterpolations.munge_data(["A","B","C"], [0.1,0.2,0.3]))
ERROR: return type Tuple{Vector{String}, Vector{Float64}} does not match inferred return type Tuple{Any, Any}
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:35
 [2] top-level scope
   @ REPL[33]:1

julia> @report_call ConstantInterpolation(["A", "B", "C"], [0.1, 0.2, 0.3])
═════ 2 possible errors found ═════
┌ ConstantInterpolation(u::Vector{String}, t::Vector{Float64}) @ DataInterpolations /Users/david/.julia/packages/DataInterpolations/dFVzN/src/interpolation_caches.jl:353
│┌ ConstantInterpolation(u::Vector{…}, t::Vector{…}; dir::Symbol, extrapolation::DataInterpolations.ExtrapolationType.T, extrapolation_left::DataInterpolations.ExtrapolationType.T, extrapolation_right::DataInterpolations.ExtrapolationType.T, cache_parameters::Bool, assume_linear_t::Float64) @ DataInterpolations /Users/david/.julia/packages/DataInterpolations/dFVzN/src/interpolation_caches.jl:360
││┌ munge_data(u::Vector{String}, t::Vector{Float64}) @ DataInterpolations /Users/david/.julia/packages/DataInterpolations/dFVzN/src/interpolation_utils.jl:120
│││┌ materialize(bc::Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{1}, Nothing, _A, <:Tuple{Vector}} where _A) @ Base.Broadcast ./broadcast.jl:872
││││┌ copy(bc::Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{…}, Tuple{…}, _A, <:Tuple{…}} where _A) @ Base.Broadcast ./broadcast.jl:897
│││││┌ copyto!(dest::BitVector, bc::Base.Broadcast.Broadcasted{…} where _A) @ Base.Broadcast ./broadcast.jl:925
││││││┌ copyto!(dest::BitVector, bc::Base.Broadcast.Broadcasted{Nothing, Tuple{Base.OneTo{…}}, _A, <:Tuple{Vector}} where _A) @ Base.Broadcast ./broadcast.jl:1002
│││││││┌ getindex(::Base.Broadcast.Broadcasted{Nothing, Tuple{…}, _A, <:Tuple{…}} where _A, ::Int64, ::CartesianIndex{0}) @ Base.Broadcast ./broadcast.jl:610
││││││││┌ _broadcast_getindex(bc::Base.Broadcast.Broadcasted{Nothing, Tuple{Base.OneTo{Int64}}, _A, Union{}} where _A, I::Int64) @ Base.Broadcast ./broadcast.jl:669
│││││││││┌ getproperty(x::Base.Broadcast.Broadcasted{Nothing, Tuple{Base.OneTo{Int64}}, _A, Union{}} where _A, f::Symbol) @ Base ./Base.jl:49
││││││││││ invalid builtin function call: Base.getfield(x::Base.Broadcast.Broadcasted{Nothing, Tuple{Base.OneTo{Int64}}, _A, Union{}} where _A, f::Symbol)
│││││││││└────────────────────
││││┌ copy(bc::Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{…}, Tuple{…}, _A, <:Tuple{…}} where _A) @ Base.Broadcast ./broadcast.jl:911
│││││┌ getindex(bc::Base.Broadcast.Broadcasted{…} where _A, Is::Int64) @ Base.Broadcast ./broadcast.jl:610
││││││┌ _broadcast_getindex(bc::Base.Broadcast.Broadcasted{…} where _A, I::Int64) @ Base.Broadcast ./broadcast.jl:669
│││││││┌ getproperty(x::Base.Broadcast.Broadcasted{…} where _A, f::Symbol) @ Base ./Base.jl:49
││││││││ invalid builtin function call: Base.getfield(x::Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{1}, Tuple{Base.OneTo{Int64}}, _A, Union{}} where _A, f::Symbol)
│││││││└────────────────────


julia> @b ([randstring(3) for _ in 1:100],rand(100)) DataInterpolations.munge_data(_[1], _[2])
7.938 μs (230 allocs: 9.188 KiB)

julia> @code_warntype ConstantInterpolation(["A", "B", "C"], [0.1, 0.2, 0.3])
MethodInstance for ConstantInterpolation(::Vector{String}, ::Vector{Float64})
  from ConstantInterpolation(u, t; dir, extrapolation, extrapolation_left, extrapolation_right, cache_parameters, assume_linear_t) @ DataInterpolations ~/.julia/packages/DataInterpolations/dFVzN/src/interpolation_caches.jl:353
Arguments
  #self#::Type{ConstantInterpolation}
  u::Vector{String}
  t::Vector{Float64}
Body::ConstantInterpolation
1 ─ %1 = DataInterpolations.:(var"#ConstantInterpolation#6")::Core.Const(DataInterpolations.var"#ConstantInterpolation#6")
│   %2 = DataInterpolations.ExtrapolationType.None::Core.Const(DataInterpolations.ExtrapolationType.None)
│   %3 = DataInterpolations.ExtrapolationType.None::Core.Const(DataInterpolations.ExtrapolationType.None)
│   %4 = DataInterpolations.ExtrapolationType.None::Core.Const(DataInterpolations.ExtrapolationType.None)
│   %5 = (%1)(:left, %2, %3, %4, false, 0.01, #self#, u, t)::ConstantInterpolation
└──      return %5

With this PR:

julia> using DataInterpolations, JET, Chairmarks, Random, Test

julia> @inferred(DataInterpolations.munge_data(["A","B","C"], [0.1,0.2,0.3]))
(["A", "B", "C"], [0.1, 0.2, 0.3])

julia> @report_call ConstantInterpolation(["A", "B", "C"], [0.1, 0.2, 0.3])
No errors detected

julia> @report_call ConstantInterpolation(["A";; "B";; "C"], [0.1, 0.2, 0.3])
No errors detected

julia> @report_call ConstantInterpolation(["A";;; "B";;; "C"], [0.1, 0.2, 0.3])
No errors detected

julia> @b ([randstring(3) for _ in 1:100],rand(100)) DataInterpolations.munge_data(_[1], _[2])
1.993 ns

julia> @code_warntype ConstantInterpolation(["A", "B", "C"], [0.1, 0.2, 0.3])
MethodInstance for ConstantInterpolation(::Vector{String}, ::Vector{Float64})
  from ConstantInterpolation(u, t; dir, extrapolation, extrapolation_left, extrapolation_right, cache_parameters, assume_linear_t) @ DataInterpolations ~/.julia/dev/DataInterpolations/src/interpolation_caches.jl:353
Arguments
  #self#::Type{ConstantInterpolation}
  u::Vector{String}
  t::Vector{Float64}
Body::ConstantInterpolation{Vector{String}, Vector{Float64}, _A, String} where _A
1 ─ %1 = DataInterpolations.:(var"#ConstantInterpolation#6")::Core.Const(DataInterpolations.var"#ConstantInterpolation#6")
│   %2 = DataInterpolations.ExtrapolationType.None::Core.Const(DataInterpolations.ExtrapolationType.None)
│   %3 = DataInterpolations.ExtrapolationType.None::Core.Const(DataInterpolations.ExtrapolationType.None)
│   %4 = DataInterpolations.ExtrapolationType.None::Core.Const(DataInterpolations.ExtrapolationType.None)
│   %5 = (%1)(:left, %2, %3, %4, false, 0.01, #self#, u, t)::ConstantInterpolation{Vector{String}, Vector{Float64}, _A, String} where _A
└──      return %5