test(tutorials): wait for state init before asserting in multiturn streaming test

The streaming test was querying client.states.list immediately after
create_task returned, before the agent's on_task_create handler ran on the
server. The sibling test_send_event_and_poll handles this with a 1s sleep;
the streaming variant was missing it and was passing by luck on faster
runners.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: declan-scale

examples/tutorials/10_async/00_base/010_multiturn/tests/test_agent.py

@@ -145,6 +145,7 @@ async def test_send_event_and_stream(self, client: AsyncAgentex, agent_id: str):
         task = task_response.result
         assert task is not None
 
+        await asyncio.sleep(1)  # wait for state to be initialized
         # Check initial state
         states = await client.states.list(agent_id=agent_id, task_id=task.id)
         assert len(states) == 1