Update event_bus.py

event_bus.py

@@ -6,7 +6,7 @@ Provides async event publishing and subscription mechanism
 import asyncio
 from typing import Dict, List, Callable, Any, Optional
 from enum import Enum
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from datetime import datetime
 import traceback
 from collections import defaultdict