Animation callbacks now pass (target, property, value) instead of (None, None)

- Add convertDrawableToPython() and convertEntityToPython() helper functions
- Add animationValueToPython() to convert AnimationValue to Python objects
- Rewrite triggerCallback() to pass meaningful data:
  - target: The animated Frame/Sprite/Grid/Entity/etc.
  - property: String property name like "x", "opacity", "fill_color"
  - final_value: float, int, tuple (for colors/vectors), or string
- Update test_animation_callback_simple.py for new signature

closes #229

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/unit/test_animation_callback_simple.py

@@ -10,11 +10,13 @@ print("=" * 30)
 # Global state to track callback
 callback_count = 0
 
-def my_callback(anim, target):
+# #229 - Animation callbacks now receive (target, property, value) instead of (anim, target)
+def my_callback(target, prop, value):
     """Simple callback that prints when animation completes"""
     global callback_count
     callback_count += 1
     print(f"Animation completed! Callback #{callback_count}")
+    print(f"  Target: {type(target).__name__}, Property: {prop}, Value: {value}")
 
 # Create scene
 callback_demo = mcrfpy.Scene("callback_demo")