fix(lint): resolve ruff errors in tests and run_tests.py

- Fix import sorting (I001)
- Remove unused imports and variables (F401, F841)
- Add noqa for test code (S106 hardcoded passwords, S314 XML parsing)
- Auto-format with ruff format

tests/apps/core/test_signals.py

@@ -88,7 +88,7 @@ class SignalDispatcherTest(TestCase):
         self.dispatcher.connect_all()
 
         # Create user to trigger signal
-        user = UserFactory.create_user()
+        UserFactory.create_user()
 
         self.assertTrue(handler_called["value"])
 
@@ -114,7 +114,7 @@ class SignalDispatcherTest(TestCase):
 
         # Create user - handler should not be called
         handler_called["value"] = False
-        user = UserFactory.create_user()
+        UserFactory.create_user()
 
         self.assertFalse(handler_called["value"])