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, 5 insertions, 3 deletions

diff --git a/packages/meshbay-hub/tests/test_groups_self_service.py b/packages/meshbay-hub/tests/test_groups_self_service.py
index f9346c1..a3a8f2d 100644
--- a/packages/meshbay-hub/tests/test_groups_self_service.py
+++ b/packages/meshbay-hub/tests/test_groups_self_service.py
@@ -1,9 +1,10 @@
 """Integration tests for group self-service: create, join, members."""
 
+from datetime import UTC
+
 import pytest
 from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
 from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey
-
 from meshbay_common.crypto import pk_to_b64
 
 
@@ -43,10 +44,11 @@ async def _create_group(client, token, name="test-group", visibility="public",
 
 async def _mark_hosted(db_session, *group_ids):
     """Pretend a node announced these groups, as /v1/nodes/ws would."""
-    from datetime import datetime, timezone
+    from datetime import datetime
+
     from meshbay_hub.db.models import Group
     for gid in group_ids:
-        (await db_session.get(Group, gid)).hosted_at = datetime.now(timezone.utc)
+        (await db_session.get(Group, gid)).hosted_at = datetime.now(UTC)
     await db_session.commit()