Apply ruff's safe autofixes.
The changes are mechanical and behaviour-preserving. Issues fixed:
- F401: remove unused imports.
- F841: drop unused local variables and assignments, including discarded
await/return values, unused "except ... as e" bindings, and unused
"with ... as name" targets.
- F541: remove the f prefix from f-strings that contain no placeholders.
- E711: compare against None with "is"/"is not" instead of "=="/"!=".
- E712: test truthiness directly instead of comparing to True.
- E713: use "x not in y" instead of "not x in y".
- E714: use "is not" instead of "not ... is".
- E731: convert lambdas bound to a name into def statements.
- W291/W293: trim trailing whitespace on touched lines.