First round of mypy fixes

[kbaikov]

This intoduces a stricter mypy config.

The first step just fixes some unused type ignores.
All according to this doc: https://mypy.readthedocs.io/en/stable/existing_code.html#getting-to-strict
Following the above mentioned doc just becauses i needed some plan of action.

@BenediktSeidl Please take a look.

Comments/suggestions welcome.

[BenediktSeidl]

just to make it clear: i have absolutely no authority here, and i'm not sure if my opinion lines up with jdavid.
but i will provide my opinion, when asked for it :-)

• i would have turned around the commits, so each commit has a chance to be green in the ci, otherwise bisecting does not work.
• i would explicitly mention warn_unused_ignores in your last commit (then first commit) because that's what you fixed there, right?

otherwise good idea to look in the official docs, maybe i should have done this, before randomly typing files.

[kbaikov]

* i would have turned around the commits, so each commit has a chance to be green in the ci, otherwise bisecting does not work.

done rearranged the commits.
I think some repos just squash all the commits in the PR automaticaly.

Whom can i ping who is the authority here? :) Perhaps @jdavid

@BenediktSeidl Also going forward i noticed a lot of C code and ffi C. I have no idea how to type the python code that calls C. Need help.