Add mypy typing support

[brent-stone]

Problem

Downstream projects using mypy and other automated tooling need can.Message to have proper type hints

Solution

Accept my pull request from brent-stone:mypy_support

Alternatives

Gradually introduce modern (3.9+) typing into the python-can package.

[brent-stone]

This is being implemented with the type hinting the dev branch. Closing.

[felixdivo]

Still thank you for your quick effort in #1226!

[zariiii9003]

@felixdivo We might need to include a py.typed file so mypy works for downstream packages. But i'm not sure if it causes problems since can.interfaces is not really well annotated.