Add ruff as formatter for Python

[dbarnett]

Fixes #223.

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[dbarnett]

@snu5mumr1k can you also approve the test workflows to run? https://github.com/google/vim-codefmt/actions/runs/10544889502

And then I think you'll need to merge it for me since I don't have write access to the repo anymore.

[dbarnett]

Hmm, FYI might be something brittle with how args are getting passed... after using this a while at one point I tried to format part of a file and it formatted every file in the repo in-place instead.

[dbarnett]

Figured it out, fixing that in #239.