Fixed crashing issue on level load/restart

I finally fixed the issue that was causing the game to crash sometimes when starting a new level or restarting the current one.

Turns out that if you use get_tree().create_tween() to tween a property of a node, then reload or switch the current scene while that tween is still active in the scene tree, godot crashes. Good to know! I replaced them all with just create_tween(), which means they'll get freed along with whatever node created them.