Add a CI to format the backend

[clarani]

Description

Add a github job to format and lint the backend. Use black (and flake8 ?)

[mikaelarguedas]

Nice coincidence I opened https://github.com/XavB64/lowtrip/pull/56 that same day.

• ruff format does only the formatting (equivalent to black)
• ruff check does the linting (flake8 + many other things)

It has the advantage of being much faster (rust-based) and feature complete than flake8.

If you like the idea I can make a separate PR for adding the linter part

[XavB64]

Can we close this issue now as ruff has been installed ?

[clarani]

Yes this issue can be closed, see https://github.com/XavB64/lowtrip/pull/69