Use Preferences.jl for compile-time CPU configuration

Minimal change to replace runtime variables in __init__ with
compile-time preferences using exact same variable names (nc, syst).

Users can now set preferences to override CPU detection:
- nc: number of cores
- syst: system threads

The __init__ function uses preferences if set, otherwise falls back
to runtime detection. This eliminates runtime overhead when preferences
are configured.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ChrisRackauckas

Project.toml

@@ -7,13 +7,15 @@ version = "0.2.6"
 CpuId = "adafc99b-e345-5852-983c-f28acb93d879"
 IfElse = "615f187c-cbe4-4ef1-ba3b-2fcf58d6d173"
 PrecompileTools = "aea7be01-6a6a-4083-8856-8a6e6704d82a"
+Preferences = "21216c6a-2e73-6563-6e65-726566657250"
 Static = "aedffcd0-7271-4cad-89d0-dc628f76c6d3"
 
 [compat]
 CpuId = "0.3"
 IfElse = "0.1"
-Static = "0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1"
+Preferences = "1"
 PrecompileTools = "1.1"
+Static = "0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1"
 julia = "1.6"
 
 [extras]

src/CPUSummary.jl

@@ -7,6 +7,7 @@ end
 using Static
 using Static: Zero, One, gt, lt
 using IfElse: ifelse
+using Preferences
 export cache_size,
   cache_linesize, cache_associativity, cache_type, cache_inclusive, num_cache, num_cores
 
@@ -52,18 +53,23 @@ if (Sys.ARCH === :x86_64)
 else
   include("generic_topology.jl")
 end
+# Load preferences at compile time with exact same names as __init__
+const nc = @load_preference("nc", nothing)
+const syst = @load_preference("syst", nothing)
+
 function __init__()
   ccall(:jl_generating_output, Cint, ()) == 1 && return
-  nc = _get_num_cores()
-  syst = Sys.CPU_THREADS::Int
-  if nc != num_l1cache()
-    @eval num_l1cache() = static($nc)
+  # Use preferences if set, otherwise detect at runtime
+  actual_nc = nc === nothing ? _get_num_cores() : nc
+  actual_syst = syst === nothing ? Sys.CPU_THREADS::Int : syst
+  if actual_nc != num_l1cache()
+    @eval num_l1cache() = static($actual_nc)
   end
-  if nc != num_cores()
-    @eval num_cores() = static($nc)
+  if actual_nc != num_cores()
+    @eval num_cores() = static($actual_nc)
   end
-  if syst != sys_threads()
-    @eval sys_threads() = static($syst)
+  if actual_syst != sys_threads()
+    @eval sys_threads() = static($actual_syst)
   end
   _extra_init()
   return nothing