refactor: implement PyArgHelpers for standardized Python argument parsing

This major refactoring standardizes how position, size, and other arguments
are parsed across all UI components. PyArgHelpers provides consistent handling
for various argument patterns:

- Position as (x, y) tuple or separate x, y args
- Size as (w, h) tuple or separate width, height args
- Grid position and size with proper validation
- Color parsing with PyColorObject support

Changes across UI components:
- UICaption: Migrated to PyArgHelpers, improved resize() for future multiline support
- UIFrame: Uses standardized position parsing
- UISprite: Consistent position handling
- UIGrid: Grid-specific position/size helpers
- UIEntity: Unified argument parsing

Also includes:
- Improved error messages for type mismatches (int or float accepted)
- Reduced code duplication across constructors
- Better handling of keyword/positional argument conflicts
- Maintains backward compatibility with existing API

This addresses the inconsistent argument handling patterns discovered during
the inheritance hierarchy work and prepares for Phase 7 documentation.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/PyDrawable.h

@@ -9,7 +9,7 @@ typedef struct {
     std::shared_ptr<UIDrawable> data;
 } PyDrawableObject;
 
-// Declare the Python type for _Drawable base class
+// Declare the Python type for Drawable base class
 namespace mcrfpydef {
     extern PyTypeObject PyDrawableType;
 }