fix: update wait for callback example

Author: bchampp

tests/integration/testdata/durable/functions/wait_for_callback/wait_for_callback.py

@@ -2,15 +2,18 @@
 from typing import Any
 
 from aws_durable_execution_sdk_python.config import WaitForCallbackConfig
-from aws_durable_execution_sdk_python.context import DurableContext
+from aws_durable_execution_sdk_python.context import (
+    DurableContext,
+    WaitForCallbackContext,
+)
 from aws_durable_execution_sdk_python.execution import durable_execution
 from aws_durable_execution_sdk_python.config import Duration
 
 logger = logging.getLogger()
 logger.setLevel(logging.INFO)
 
 
-def external_system_call(callback_id: str) -> None:
+def external_system_call(callback_id: str, _context: WaitForCallbackContext) -> None:
     """Simulate calling an external system with callback ID."""
     # In real usage, this would make an API call to an external system
     # passing the callback_id for the system to call back when done