Versioned enumerator for RecyclableList implemented. Benchmarks & tests added.

Recyclable.Collections/RecyclableList.VersionedEnumerator.cs

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+using System.Collections;
+using System.Diagnostics.Contracts;
+using System.Runtime.InteropServices;
+
+namespace Recyclable.Collections
+{
+	public partial class RecyclableList<T> : IVersionedList<T>
+	{
+		VersionedEnumerator IVersionedList<T>.GetEnumerator() => new(this);
+
+		[StructLayout(LayoutKind.Sequential, Pack = 1)]
+		public struct VersionedEnumerator : IEnumerator<T>
+		{
+			private int _currentItemIndex;
+			private readonly ulong _enumeratorVersion;
+			private readonly RecyclableList<T> _list;
+
+#nullable disable
+			// [Pure]
+			public readonly T Current => _enumeratorVersion == _list._version ? _list._memoryBlock[_currentItemIndex - 1] : throw new InvalidOperationException();
+			// [Pure]
+			readonly object IEnumerator.Current => _enumeratorVersion == _list._version ? _list._memoryBlock[_currentItemIndex - 1] : throw new InvalidOperationException();
+#nullable restore
+
+			public bool MoveNext()
+			{
+				if (_enumeratorVersion != _list._version)
+				{
+					throw new InvalidOperationException();
+				}
+
+				Contract.EndContractBlock();
+
+				if (_currentItemIndex < _list._count)
+				{
+					_currentItemIndex++;
+					return true;
+				}
+
+				return false;
+			}
+
+			public VersionedEnumerator(RecyclableList<T> list)
+			{
+				_currentItemIndex = 0;
+				_list = list;
+				_enumeratorVersion = list._version;
+			}
+
+			public readonly void Dispose()
+			{
+			}
+
+			void IEnumerator.Reset()
+			{
+				if (_enumeratorVersion != _list._version)
+				{
+					throw new InvalidOperationException();
+				}
+
+				_currentItemIndex = 0;
+			}
+		}
+	}
+}