style: repo-wide lint pass — make the lint gate green again

Push builds have been RED on the lint step since ~build 209 from accumulated
formatting drift. This is the mechanical cleanup: ruff format + ruff --fix
(UP038 isinstance unions, SIM105 contextlib.suppress, UP031 f-strings, SIM115
tempfile context manager), shfmt -i 2 -ci, nixpkgs-fmt/statix/deadnix (merged
attrsets, dropped unused lib args), yamllint, and shell quoting fixes in
tests/lasuite-docs/setup_custom_tests.sh. No behaviour changes intended;
lint: PASS, unit tests: 138 passed.

tests/mumble/functional/test_protocol_handshake.py

@@ -25,7 +25,7 @@ def test_handshake_completes_with_channel_presence(live_app):
     assert r["server_version"] is not None, "server did not send a Version message"
     assert r["auth_accepted"], f"authentication not accepted — {r.get('error')}"
     # Channel presence: the server must expose at least the root channel (beyond a bare TCP open).
-    assert len(r["channels"]) >= 1, (
-        f"server reported no channels (expected >=1 root channel) — {r!r}"
-    )
+    assert (
+        len(r["channels"]) >= 1
+    ), f"server reported no channels (expected >=1 root channel) — {r!r}"
     assert r["server_sync"], f"ServerSync handshake did not complete — {r.get('error')}"