infrastructure-resource-leak-opensearchvectorclient-does-not-close-the-async-cl-270acd22

THEN Implement cleanup using try...finally pattern in the fixture or explicitly call client._os_async_client.close() when ending sessions. Ensure the async client is closed after each operation to prevent resource leaks.

```python
@pytest.fixture()
def os_store(index_name: str) -> Generator[OpensearchVectorStore, None, None]:
    client = OpensearchVectorClient(endpoint="localhost:9200", index=index_name, dim=3)
    try:
        yield OpensearchVectorStore(client)
    finally:
        evt_loop.run_until_complete(client._os_client.indices.delete(index=index_name))
        evt_loop.run_until_complete(client._os_client.close())
```