[Feature request] Add py.typed marker

[drewsilcock]

This package has type hints, but none of them are available to codebases using this package as the py.typed marker is not present. All you need to do is add an empty file called py.typed and all library users can enjoy the benefits of seeing the type hints inside the library. You may also need to update the setup.cfg to ensure the py.typed file is included in the package bundle.

See: https://peps.python.org/pep-0561/#packaging-type-information