Pools made thread static. Various small optimizations. "in" parameter added to read-only method parameters

PerfectNumbers.Core/ThreadStaticPools.cs

@@ -0,0 +1,41 @@
+using System.Buffers;
+using System.Runtime.CompilerServices;
+
+namespace PerfectNumbers.Core
+{
+    public static class ThreadStaticPools
+    {
+		[ThreadStatic]
+		private static ArrayPool<FactorEntry>? _factorEntryPool;
+		public static ArrayPool<FactorEntry> FactorEntryPool
+		{
+			[MethodImpl(MethodImplOptions.AggressiveInlining)]
+			get
+			{
+				return _factorEntryPool ??= ArrayPool<FactorEntry>.Create();
+			}
+		}
+
+		[ThreadStatic]
+		private static ArrayPool<FactorEntry128>? _factorEntry128Pool;
+		public static ArrayPool<FactorEntry128> FactorEntry128Pool
+		{
+			[MethodImpl(MethodImplOptions.AggressiveInlining)]
+			get
+			{
+				return _factorEntry128Pool ??= ArrayPool<FactorEntry128>.Create();
+			}
+		}
+
+		[ThreadStatic]
+		private static ArrayPool<ulong>? _ulongPool;
+		public static ArrayPool<ulong> UlongPool
+		{
+			[MethodImpl(MethodImplOptions.AggressiveInlining)]
+			get
+			{
+				return _ulongPool ??= ArrayPool<ulong>.Create();
+			}
+		}
+	}
+}