Add pre-commit

[hoxbro]

Adding pre-commit. The pre-commit itself is inspired by Holoviews, though I tried adding ruff instead of flake8, this can of course be reversed if needed.

I can also add isort if needed.

[maximlt]

Please let's not use ruff in hvPlot. It's:

• too new
• more useful for large code bases
• an incomplete re-implementation of flake8 (why not making flake8 faster instead?)

doit test_flakes should also be updated.