Added pools, IndexedFishMap, IndexedFishSet, fixed bugs related to FishTable.Remove, added Preview.png, various smaller additions, some refactoring too

Source/FisheryLib/Pools/PooledIList.cs

@@ -0,0 +1,49 @@
+// Copyright (c) 2023 bradson
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+using System.Collections;
+using System.Runtime.CompilerServices;
+
+namespace FisheryLib.Pools;
+
+public record struct PooledIList<T>() : IDisposable where T : IList, new()
+{
+	public T List = Get();
+	
+	private static T?[] _freeItems = new T[4];
+	private static int _freeItemCount;
+
+	public void Dispose()
+	{
+		if (List == null)
+			return;
+		
+		Return(List);
+		List = default!;
+	}
+
+	public static T Get()
+	{
+		if (_freeItemCount == 0)
+			return Reflection.New<T>();
+		
+		var freeItem = _freeItems[--_freeItemCount];
+		_freeItems[_freeItemCount] = default;
+		return freeItem!;
+	}
+
+	public static void Return(T item)
+	{
+		item.Clear();
+		
+		if (++_freeItemCount >= _freeItems.Length)
+			ExpandFreeItems();
+
+		_freeItems[_freeItemCount - 1] = item;
+	}
+
+	[MethodImpl(MethodImplOptions.NoInlining)]
+	private static void ExpandFreeItems() => Array.Resize(ref _freeItems, _freeItems.Length << 1);
+}