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/mailu/functional/test_mailbox.py

@@ -24,6 +24,6 @@ def test_create_mailbox_and_read_back(live_app):
 
     cfg = _mailu.config_export(live_app)
     emails = _mailu.user_emails(cfg)
-    assert email in emails, (
-        f"created mailbox {email} not present in mailu config-export users {emails}"
-    )
+    assert (
+        email in emails
+    ), f"created mailbox {email} not present in mailu config-export users {emails}"