refactor: use workflow.get_external_workflow_handle instead of manual client connection for signaling callbacks

temporal/workflow.py

@@ -88,9 +88,9 @@ class SimulationWorkflow:
         )
         
         if sim_data.get("CallbackWorkflowId"):
-            client = await Client.connect(TEMPORAL_URL)
-            handle = client.get_workflow_handle(sim_data["CallbackWorkflowId"])
-
+            handle = workflow.get_external_workflow_handle(
+                sim_data["CallbackWorkflowId"]
+            )
             await handle.signal("notify_done")