perf!: events refactored throughout all the project to use Event<> class

All delegate events are refactored to use the Event<TSender> and Event<TSender, TArgument> for performance issues regarding delegate events creating garbage, also this gives us better control on event invocation since C# Delegates did also create unnecessary garbage during Delegate.DynamicInvoke

Engine.Core/Abstract/Assignable/IAssignable.cs

@@ -8,7 +8,7 @@ public interface IAssignable
     /// <summary>
     /// Event triggered when the <see cref="IAssignable"/>'s fields are unassigned and completely ready to recycle.
     /// </summary> 
-    event UnassignEventHandler? OnUnassigned;
+    Event<IAssignable>? OnUnassigned { get; }
 
     /// <summary>
     /// Unassign <see cref="IAssignable"/>'s all fields and make it ready to recycle.
@@ -17,6 +17,4 @@ public interface IAssignable
     /// <see cref="true"/>, if the fields are unsigned successfully, <see cref="false"/> if not.
     /// </returns>
     bool Unassign();
-
-    delegate void UnassignEventHandler(IAssignable sender);
 }