Mark python cp_model module as type hinted

[bodograumann]

What language and solver does this apply to?
Python, packaging

Describe the problem you are trying to solve.
I want to typecheck my code, which is using from ortools.sat.python import cp_model, with mypy.

Currently mypy just gives an error:

error: Skipping analyzing "ortools.sat.python": module is installed, but missing library stubs or py.typed marker [import]

Cff.:

• https://mypy.readthedocs.io/en/stable/running_mypy.html?highlight=py.typed#missing-library-stubs-or-py-typed-marker
• https://peps.python.org/pep-0561/

Describe the solution you'd like
Please add the py.typed marker, so that mypy accepts the module as typed.

Describe alternatives you've considered
Unfortunately it is currently not possible to force the mypy behaviour. Cf. python/mypy#8545