[BLD] Python & misc lint fixes

[codetheweb]

This enables all lints except check-yamland mypy, both of which seem to require quite a few manual changes.

I'll create issues to enable those after merging this.

Outside of removing a few unused imports & the updates to the lint config/workflow, the changes in this PR were entirely made by automated tooling.

[github-actions]

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• Can you think of any use case in which the code does not behave as intended? Have they been tested?
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