Add type annotations to porcelain.py functions

Add Union[str, os.PathLike, BaseRepo] type annotations to 74 functions
in porcelain.py to improve type inference. This helps tools like
dissolve perform better type introspection when migrating deprecated
API calls.

While most functions now have proper type annotations, there are still
3 specific calls that fail type introspection in porcelain.py itself,
likely due to tool-specific issues with the file.