Some code quality ideas

[arvidj]

I'm wondering what your general feeling would be about:

• Using poetry for dependency management for those not using nix.
• Using a code formatter like black.
• Using typehints and typechecker like mypy. I've experimented using pyannotate to annotate tests/gitlab_api_mock.py (it required a fair deal of manual annotation though) and found the resulting file far easier to understand.

[JohnVillalovos]

#291 Has some poetry work going on there.

[arvidj]

FYI, black is now stable , and is used by e.g. Drupal.

[nejch]

I guess all of this is also related to https://github.com/smarkets/marge-bot/issues/295, as there's more quality of life stuff for developers discussed there, but there's a bit of a backlog already.