Initial framework for adding type-hints and added type-hints to version.py

[JohnVillalovos]

This is adding the initial framework for adding type-hints. It adds the running of mypy and type-checks nothing in the first commit.

Then adds type-checking of the file imapclient/version.py and others can use that as an example of how to add type-hints by updating pyproject.toml

[NicolasLM]

Looks good to me, although given the low activity on IMAPClient in the past few of years, I doubt type hints will ever be populated on a significant portion of the code.

[mjs]

Still worth it I think