Report scipy version in tests, add ruff configuration

[lfarv]

This PR adds a printout of the scipy version in the output of pytest: the will ease the tracking of sudden test failures as it recently happened.

It also adds a configuration of the ruff formatter/linter in pyproject.toml. ruff is equivalent to black as a formatter (with ruff format file.py), but also suggest code improvements or simplifications (with ruff check file.py). Its use is recommended as its suggestions are usually valuable (but not mandatory!)