updates for 2025

[slingamn]

@hbmartin this is mostly your code from #14, but I went over it line by line and removed some things:

1. I didn't see a strong reason to enforce black. Users who are vendoring mureq should be able to either reformat it themselves, or exclude it from their formatting rules.
2. Same for ruff given that it needs mureq-specific configuration in any case (users can add it to their exclude rules)
3. I only annotated the public API
4. CI does not run the integration tests (they still run from make test), as per the caution against running them automatically in the README

This also fixes #13 and #15