chore: Avoid mutable default arguments in local_eval_service and runners

Changed default values for `session_service`, `artifact_service`, and `run_config` from instances of mutable classes to `None`. Instances are now created within the function body if the argument is not provided, preventing unexpected shared state across function calls.

PiperOrigin-RevId: 804624564

tests/unittests/cli/test_fast_api.py

@@ -21,7 +21,6 @@ import sys
 import tempfile
 import time
 from typing import Any
-from typing import Optional
 from unittest.mock import MagicMock
 from unittest.mock import patch
 
@@ -121,9 +120,8 @@ async def dummy_run_async(
     session_id,
     new_message,
     state_delta=None,
-    run_config: Optional[RunConfig] = None,
+    run_config: RunConfig = RunConfig(),
 ):
-  run_config = run_config or RunConfig()
   yield _event_1()
   await asyncio.sleep(0)