chore: default to pytest asyncio-mode=auto (#2730)

# What does this PR do?

previously, developers who ran `./scripts/unit-tests.sh` would get
`asyncio-mode=auto`, which meant `@pytest.mark.asyncio` and
`@pytest_asyncio.fixture` were redundent. developers who ran `pytest`
directly would get pytest's default (strict mode), would run into errors
leading them to add `@pytest.mark.asyncio` / `@pytest_asyncio.fixture`
to their code.

with this change -
- `asyncio_mode=auto` is included in `pyproject.toml` making behavior
consistent for all invocations of pytest
- removes all redundant `@pytest_asyncio.fixture` and
`@pytest.mark.asyncio`
 - for good measure, requires `pytest>=8.4` and `pytest-asyncio>=1.0`

## Test Plan

- `./scripts/unit-tests.sh`
- `uv run pytest tests/unit`

tests/integration/agents/test_persistence.py

@@ -44,7 +44,6 @@ def common_params(inference_model):
     )
 
 
-@pytest.mark.asyncio
 @pytest.mark.skip(reason="This test needs to be migrated to api / client-sdk world")
 async def test_delete_agents_and_sessions(self, agents_stack, common_params):
     agents_impl = agents_stack.impls[Api.agents]
@@ -73,7 +72,6 @@ async def test_delete_agents_and_sessions(self, agents_stack, common_params):
     assert agent_response is None
 
 
-@pytest.mark.asyncio
 @pytest.mark.skip(reason="This test needs to be migrated to api / client-sdk world")
 async def test_get_agent_turns_and_steps(self, agents_stack, sample_messages, common_params):
     agents_impl = agents_stack.impls[Api.agents]

tests/integration/inspect/test_inspect.py

@@ -4,20 +4,17 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
-import pytest
 from llama_stack_client import LlamaStackClient
 
 from llama_stack import LlamaStackAsLibraryClient
 
 
 class TestInspect:
-    @pytest.mark.asyncio
     def test_health(self, llama_stack_client: LlamaStackAsLibraryClient | LlamaStackClient):
         health = llama_stack_client.inspect.health()
         assert health is not None
         assert health.status == "OK"
 
-    @pytest.mark.asyncio
     def test_version(self, llama_stack_client: LlamaStackAsLibraryClient | LlamaStackClient):
         version = llama_stack_client.inspect.version()
         assert version is not None

tests/integration/providers/test_providers.py

@@ -4,14 +4,12 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
-import pytest
 from llama_stack_client import LlamaStackClient
 
 from llama_stack import LlamaStackAsLibraryClient
 
 
 class TestProviders:
-    @pytest.mark.asyncio
     def test_providers(self, llama_stack_client: LlamaStackAsLibraryClient | LlamaStackClient):
         provider_list = llama_stack_client.providers.list()
         assert provider_list is not None

tests/integration/providers/utils/sqlstore/test_authorized_sqlstore.py

@@ -88,7 +88,6 @@ async def cleanup_records(sql_store, table_name, record_ids):
             pass
 
 
-@pytest.mark.asyncio
 @pytest.mark.parametrize("backend_config", BACKEND_CONFIGS)
 @patch("llama_stack.providers.utils.sqlstore.authorized_sqlstore.get_authenticated_user")
 async def test_authorized_store_attributes(mock_get_authenticated_user, authorized_store, request):
@@ -183,7 +182,6 @@ async def test_authorized_store_attributes(mock_get_authenticated_user, authoriz
         await cleanup_records(authorized_store.sql_store, table_name, ["1", "2", "3", "4", "5", "6"])
 
 
-@pytest.mark.asyncio
 @pytest.mark.parametrize("backend_config", BACKEND_CONFIGS)
 @patch("llama_stack.providers.utils.sqlstore.authorized_sqlstore.get_authenticated_user")
 async def test_user_ownership_policy(mock_get_authenticated_user, authorized_store, request):