Update code review comments

Author: goanpeca

ignite/engine/engine.py

@@ -433,15 +433,14 @@ def _fire_event(self, event_name: Any, *event_args: Any, **event_kwargs: Any) ->
         self.last_event_name = event_name
         for func, args, kwargs in self._event_handlers[event_name]:
             kwargs.update(event_kwargs)
-            # Resolve weak references if present
             if args and isinstance(args[0], weakref.ref):
                 resolved_engine = args[0]()
                 if resolved_engine is None:
-                    # Engine was garbage collected, skip this handler
-                    continue
+                    raise RuntimeError("Engine reference not resolved. Cannot execute event handler.")
                 first, others = ((resolved_engine,), args[1:])
             else:
-                first, others = ((args[0],), args[1:]) if (args and args[0] == self) else (tuple(), args)
+                raise ValueError("Invalid event handler.")
+
             func(*first, *(event_args + others), **kwargs)
 
     def fire_event(self, event_name: Any) -> None: