Add py.typed marker for MyPy support

[TaneliEDRM]

📝 Description of the feature

Code seems to be already typed, but the py.typed marker is missing so MyPy raises an error.

Static type analysis is part of most modern python projects and it would be a great addition to use it in projects using PyAnsys packages.

💡 Steps for implementing the feature

Add py.typed to library.

🔗 Useful links and references

https://peps.python.org/pep-0561/
https://mypy-lang.org/

[RobPasMue]

Thanks for opening this issue @TaneliEDRM ! Good catched, we never included it despite using type hints. Let me add it!