Isolate CPU divisor pools per thread

PerfectNumbers.Core/ThreadLocalArrayPool.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Buffers;
+using System.Runtime.CompilerServices;
+
+namespace PerfectNumbers.Core;
+
+internal static class ThreadLocalArrayPool<T>
+{
+    [ThreadStatic]
+    private static ArrayPool<T>? s_threadPool;
+
+    public static ArrayPool<T> Shared
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get
+        {
+            ArrayPool<T>? pool = s_threadPool;
+            if (pool is null)
+            {
+                pool = ArrayPool<T>.Create();
+                s_threadPool = pool;
+            }
+
+            return pool;
+        }
+    }
+}