fix: Execute event manager callbacks in asyncio thread (#5150)

Execute event manager callbacks in asyncio thread

src/backend/tests/unit/custom/custom_component/test_component_events.py

@@ -1,4 +1,5 @@
 import asyncio
+import time
 from typing import Any
 from unittest.mock import MagicMock
 
@@ -17,6 +18,11 @@ async def create_event_queue():
     return asyncio.Queue()
 
 
+def blocking_cb(manager, event_type, data):
+    time.sleep(0.01)
+    manager.send_event(event_type=event_type, data=data)
+
+
 class ComponentForTesting(Component):
     """Test component that implements basic functionality."""
 
@@ -39,6 +45,8 @@ async def test_component_message_sending():
     queue = await create_event_queue()
     event_manager = EventManager(queue)
 
+    event_manager.register_event("on_message", "message", callback=blocking_cb)
+
     # Create component
     component = ComponentForTesting()
     component.set_event_manager(event_manager)
@@ -196,7 +204,8 @@ async def test_component_streaming_message():
     """Test component's streaming message functionality."""
     queue = await create_event_queue()
     event_manager = EventManager(queue)
-    event_manager.register_event("on_token", "token")
+
+    event_manager.register_event("on_token", "token", blocking_cb)
 
     # Create a proper mock vertex with graph and flow_id
     vertex = MagicMock()