Copy masks in setaffinities to avoid mutating user data

ThreadPinningCore.setaffinity(mask) extends the mask in-place via append!
when mask length < uv_cpumask_size(). This caused setaffinities to mutate
the caller's mask objects, leading to test failures when comparing the
mutated masks (now extended to uv_cpumask_size) against fresh getaffinity()
results (truncated to cpuidlimit/Sys.CPU_THREADS).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: carstenbauer

src/pinning.jl

@@ -311,7 +311,7 @@ function setaffinities(masks; threadpool::Symbol = :default)
         throw(ArgumentError("Number of masks ($(length(masks))) must match the number of " *
                             "threads ($(length(tids))) in the `$(threadpool)` threadpool."))
     for (i, threadid) in pairs(tids)
-        setaffinity(masks[i]; threadid)
+        setaffinity(copy(masks[i]); threadid)
     end
     return
 end