[Python] Add `py.typed` marked file to enable type checking

The Python package is missing a [`py.typed` marker file](https://typing.python.org/en/latest/spec/distributing.html#packaging-type-information). This hampers type checking and leads to CI pipeline faults (e.g., Mypy warning).

Start by locating the Python package's packaging configuration and how package data is included. Add the py.typed marker described in the issue, then run the relevant MyPy or CI checks to confirm the type-checking warning is resolved.

Written by the indexing model from the issue text.