docs(toolbox-core): Update auth module docstring to guide using context manager.

Author: anubhav756

packages/toolbox-core/src/toolbox_core/auth_methods.py

@@ -20,11 +20,11 @@
 from toolbox_core import auth_methods
 
 auth_token_provider = auth_methods.aget_google_id_token
-toolbox = ToolboxClient(
+async with ToolboxClient(
     URL,
     client_headers={"Authorization": auth_token_provider},
-)
-tools = await toolbox.load_toolset()
+) as toolbox:
+    tools = await toolbox.load_toolset()
 """
 
 from datetime import datetime, timedelta, timezone