lint: fix mypy errors and use Ruff

In a recent patch, python-linting job failed due to "wrong imports order", even that I am using ruff in my IDE to write code.

As ruff is a linter and a formatter at the same time, with its own import sort algorithm. I think it is better to stick with it due to simplicity.

Keeping mypy, since it is still peculiarly good for type checking.