libfaketime and python-libfaketime seem to cause our CI to fail when
used in conjunction with `uv`. This changes the way the tests are done
so they don't require libfaketime anymore.
- Replace black by ruff, as it's quicker ;
- Use `uv` wherever possible as a replacement for pip, as it's way faster to run, add an `uv.lock` file which will be synced before the releases and published here ;
- Remove tox, it's too complex for this project and can easily be replaced by `uv` ;
- Apply `ruff` formatting ;
- Update the makefile accordingly ;
- Update the CI accordingly
