pytest-asyncio 0.23+ requires @pytest_asyncio.fixture for async fixtures

Starting with pytest-asyncio 0.23, async fixtures decorated with @pytest.fixture are no longer auto-detected. The auto mode only applies @pytest.mark.asyncio to async test functions but async fixtures still need the explicit @pytest_asyncio.fixture decorator. Without it, the async generator or coroutine is returned directly as the fixture value (not awaited), causing TypeError or coroutine was never awaited warnings.