feat: added a wip nested coroutine manager

This coroutine manager allows for nested IEnumerators, however it is experimental at the moment.

Engine.Core/Systems/Abstract/ICoroutineManager.cs

@@ -0,0 +1,9 @@
+using System.Collections;
+
+namespace Engine.Core;
+
+public interface ICoroutineManager
+{
+    IEnumerator StartCoroutine(IEnumerator enumerator);
+    void StopCoroutine(IEnumerator enumerator);
+}