Added unit tests for event registration, dispatching, and context infrastructure.

- EventRegistry.get_all() now deep-copies handler lists so callers cannot mutate internal state.

owlbot/registries/events.py

@@ -138,7 +138,9 @@ class EventRegistry:
 
         :return: Dict mapping event type values to handler lists.
         """
-        return self._handlers.copy()
+        return {
+            event_type: entries.copy() for event_type, entries in self._handlers.items()
+        }
 
     def get_handler_module(self, handler: EventHandler) -> str | None:
         """