fix(tests): Enable background loop in emit_event test to fix queue assertion

The test_emit_event test was failing because it expected the event to be
placed in the queue, but emit_event() has conditional logic:
- When _running=False (test mode): processes event immediately
- When _running=True (production): queues event for async processing

The test creates a CacheInvalidationManager with _running=False by default,
so events get processed immediately rather than queued. The test then
checked if event_queue.empty(), which failed because the queue was never used.

Fix: Set manager._running = True before calling emit_event() so the event
gets queued as the test expects.

Result: All 82 tests now passing ✅

Author: MarcoPolo483

tests/test_cache_layer.py

@@ -314,6 +314,8 @@ async def test_register_handler(self):
     async def test_emit_event(self):
         """Test event emission"""
         manager = CacheInvalidationManager()
+        # Enable background loop so events get queued (not processed immediately)
+        manager._running = True
 
         event = InvalidationEvent(
             change_type='update',