- Replace Updatable interface with Update interface
- Add Pose<P> template interface for pose management
- Add PosedData<P> abstract base class for setup data
- Add Posed<D,P,A> base class linking data, pose, and applied states
- Add PosedActive<D,P,A> extending Posed with active state management
- Update spine.h to include new pose system headers
This implements the foundational pose architecture required for the 4.3-beta
constraint system overhaul. The new pose-based system provides better separation
of concerns and enables more flexible constraint management.