Enable minimal ruff check in CI

[rolandwalker]

Description

• remove unused imports from main.py
• remove unneeded pass statement
• clean up unneeded list literals
• remove needless whitespace
• call endswith() only once with a tuple
• fix needless generators, rule C400
• fix needless list comprehension
• prefer generator over map+lambda
• disable sufficient rules for ruff check to pass
• proactively add some known-first-party imports
• enable ruff check in CI, modifying tox.ini such that files are checked but not modified

While there are many fixes, this leaves some individual rules disabled, to be enabled one-by-one in future PRs. The key thing is that checks are turned on in CI.

Checklist

• I've added this contribution to the changelog.md.
• I've added my name to the AUTHORS file (or it's already there).