style: ruff's own fixes, mechanically applied

`ruff check .` had gone unrun long enough to report 568 errors, which is the
same as having no linter: the next real finding would have been invisible in the
noise. This is the 521 it fixes by itself, in 173 files, and nothing else — the
98 it cannot fix are the next commit.

What actually changed: import sorting (225), imports nobody used (87, none of
them a re-export — no `__init__.py` is touched, which was the one way this could
have broken an import elsewhere), `datetime.timezone.utc` to `datetime.UTC` (69)
and `asyncio.TimeoutError` to `TimeoutError` (18), both plain aliases on the 3.12
this project requires, `Optional[X]` to `X | None` (24), and f-strings with
nothing to interpolate (19).

Checked rather than assumed: every module in the three packages still imports,
and the suite is 2893 passed — the same count, test for test, as the merge
before it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 3 insertions, 4 deletions

diff --git a/packages/meshbay-hub/tests/test_group_leave_and_quota.py b/packages/meshbay-hub/tests/test_group_leave_and_quota.py
index 4431f53..8af830d 100644
--- a/packages/meshbay-hub/tests/test_group_leave_and_quota.py
+++ b/packages/meshbay-hub/tests/test_group_leave_and_quota.py
@@ -14,13 +14,12 @@ removes them, and whoever left still holds the group key they were served.
 
 import base64
 import hashlib
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 
 import pytest
-from sqlalchemy import select
-
 from meshbay_hub.api.groups import MAX_PUBLIC_GROUPS
 from meshbay_hub.db.models import Group, GroupMember, User
+from sqlalchemy import select
 
 
 def _auth_key(password: str, username: str) -> str:
@@ -61,7 +60,7 @@ async def test_a_member_can_leave(client, db_session):
     # Marked hosted, or the member would not see the group in the first place
     # and the assertion below would hold whether or not leaving worked.
     g = await db_session.get(Group, gid)
-    g.hosted_at = datetime.now(timezone.utc)
+    g.hosted_at = datetime.now(UTC)
     await db_session.commit()
 
     before = await client.get("/v1/groups/mine", headers=member)