chore: ruff up the codebase

[dimaqq]

What this PR does

In short, we'll be relying on ruff via pre-commit as opposed to flake8 via tox.

• switches from flake8 to ruff
• reformats the source code
• reformats the docstrings where safe, conservatively
• resolves ruff complaints where that's straightforward
• silences with a FIXME where public API could break or code change is not obvious or where too much manual work is required, those can be fixed in separate PRs
• updates the CI and docs for the above

Check list

• pre-commit config
• ruff over the codebase
• resolve or silence errors
• kill old linter and github actions
• GitHub actions to check pre-commit
• run pre-commit after codegen
• add to docs

[dimaqq]

I've reviewed the full diff on github.

[james-garner-canonical]

Went through this with Dima in a video call, and I think we're good to land this now

[dimaqq]

/merge