Strict linting

[Epse]

Makes the ruff linter very strict, and thus very helpful.
Most rules that are applicable to our codebase have been enabled, with the following exceptions:

• DTZ: there are exactly two uses of datetime in the codebase, in the comparison of token expiry, naive is fine there
• D: We acknowledge that our documentation is probably insufficient, but this linting is too aggressive at this time

For the relevant rules, fixes are included

Also adds the lint check to the pre-commit hook, as that had gotten forgotten before.