perf: implemented fast list with index mapping

Engine.Core/Helpers/FastList.cs

@@ -0,0 +1,74 @@
+using System.Collections;
+using System.Collections.Generic;
+
+namespace Engine.Core;
+
+public class FastList<T> : IReadOnlyList<T>, IEnumerable<T> where T : notnull
+{
+    private readonly List<T> items = [];
+    private readonly Dictionary<T, int> indexMap = [];
+
+    public int Count => items.Count;
+
+    public T this[int index] => items[index];
+
+    public void Add(T item)
+    {
+        indexMap[item] = items.Count;
+        items.Add(item);
+    }
+
+    public void RemoveAt(int i) => Remove(items[i], i);
+    public bool Remove(T item)
+    {
+        if (!indexMap.TryGetValue(item, out int index))
+            return false;
+
+        Remove(item, index);
+
+        return true;
+    }
+
+    private void Remove(T item, int index)
+    {
+        int lastIndex = items.Count - 1;
+        T lastItem = items[lastIndex];
+
+        items[index] = lastItem;
+        indexMap[lastItem] = index;
+
+        items.RemoveAt(lastIndex);
+        indexMap.Remove(item);
+    }
+
+    public void Insert(int index, T item)
+    {
+        items.Insert(index, item);
+
+        for (int i = index; i < items.Count; i++)
+            indexMap[items[i]] = i;
+    }
+
+    public void Clear()
+    {
+        items.Clear();
+        indexMap.Clear();
+    }
+
+    public bool Contains(T item) => indexMap.ContainsKey(item);
+
+    public int BinarySearch(T item, IComparer<T>? comparer = null) => items.BinarySearch(item, comparer);
+    public void Sort(IComparer<T> comparer)
+    {
+        items.Sort(comparer);
+
+        for (int i = 0; i < items.Count; i++)
+            indexMap[items[i]] = i;
+    }
+
+    public IEnumerator<T> GetEnumerator() => items.GetEnumerator();
+    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+
+    public FastList() { }
+    public FastList(int count) { items.Capacity = count; }
+}