[1.21.X] Improved Event System

[RealMangorage]

This PR aims to improve the event system to make it possible for more flexible systems, such as being able to put additional parameters/return types.

E.G you could do in this system:
EnterRoomEvent

  boolean handle(ServerLevel level, RoomInstance room, ItemStack upgrade);
  
  boolean being if cancelled.

I can make adjustments if needed.