Monkey Patch support + Robust callback tracking

McRogueFace needs to accept callable objects (properties on C++ objects)
and also support subclassing (getattr on user objects). Only direct
properties were supported previously, now shadowing a callback by name
will allow custom objects to "just work".
- Added CallbackCache struct and is_python_subclass flag to UIDrawable.h
- Created metaclass for tracking class-level callback changes
- Updated all UI type init functions to detect subclasses
- Modified PyScene.cpp event dispatch to try subclass methods

tests/unit/test_scene_object_api.py

@@ -153,8 +153,8 @@ def test_scene_subclass():
             self.exit_count += 1
             print(f"    GameScene.on_exit() called (count: {self.exit_count})")
 
-        def on_keypress(self, key, action):
-            print(f"    GameScene.on_keypress({key}, {action})")
+        def on_key(self, key, action):
+            print(f"    GameScene.on_key({key}, {action})")
 
         def update(self, dt):
             self.update_count += 1