Support serialization metadata on template typedefs

[dellaert]

Summary

• parse @serializable on template typedef instantiations
• synthesize the wrapper serialization marker only for the annotated alias
• reuse the existing Python and MATLAB serialization generation paths
• document and test the new annotation

This lets clients expose several specializations of one class template while enabling serialization for an individual public alias without changing the underlying C++ template declaration.

Testing

• uv run pytest tests -q (134 passed)
• git diff master...HEAD --check