Adding a formatter/check like astyle/codecheck

[Iximiel]

Hi @gtribello, look if you like this:

I added a formatter and a static check that helps in looking for errors (such as unused variables/imports, wrong variables hidden in raised exceptions, it seems to dislike using 'l' as variable since it is similar to 'I', and so on)
This should help in tracking future merges/changes like we do with astyle and codecheck in plumed

I chose to use and indent of 2 spaces, but this is an opinionated choice of mine, I can change it

To format things on your pc you simply need to run tox in the home directory of the project:
it will

• format
• check for some python errors
• run the test locally
  in this order

to run the check alone you can run ruff format (or tox -e format), ruff check (or tox -e linting)

The CI will softly enforce the check and the formatting, but with no interference in the the old tests