Remove rufo gem

What does this MR do and why?

Rufo was used in lefthook.yml but never checked on CI (removed in !231 (merged)) nor the current rufo check succeeded forcing developers to git push --no-verify.

Remove the rufo gem and re-enable (and auto-correct) RuboCop rules which were disabled to respect rufo's style.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.