Add Ruff configuration file

[AA-Turner]

No description provided.

[hugovk]

We already have a pyproject.toml for pytest config, can we have the Ruff config in the same file? And other tool config could live there too.

[AA-Turner]

I prefer keeping tool configuration in dedicated files (where in a reasonable (non-INI) format). pyproject.toml files get hard to read as they get hundreds of lines long!

pytest only supports pytest.ini as a standalone format, hence keeping it in pyproject.toml, which otherwise doesn't make sense for this project, as it's not intended for distribution.

A