chore(misc): make tests and starter faster (#3042)

A bunch of miscellaneous cleanup focusing on tests, but ended up
speeding up starter distro substantially.

- Pulled llama stack client init for tests into `pytest_sessionstart` so
it does not clobber output
- Profiling of that told me where we were doing lots of heavy imports
for starter, so lazied them
- starter now starts 20seconds+ faster on my Mac
- A few other smallish refactors for `compat_client`

tests/integration/vector_io/test_openai_vector_stores.py

@@ -11,10 +11,8 @@ from io import BytesIO
 import pytest
 from llama_stack_client import BadRequestError, LlamaStackClient
 from openai import BadRequestError as OpenAIBadRequestError
-from openai import OpenAI
 
 from llama_stack.apis.vector_io import Chunk
-from llama_stack.core.library_client import LlamaStackAsLibraryClient
 
 logger = logging.getLogger(__name__)
 
@@ -69,19 +67,6 @@ def skip_if_provider_doesnt_support_openai_vector_stores_search(client_with_mode
     )
 
 
-@pytest.fixture
-def openai_client(client_with_models):
-    base_url = f"{client_with_models.base_url}/v1/openai/v1"
-    return OpenAI(base_url=base_url, api_key="fake")
-
-
-@pytest.fixture(params=["openai_client", "llama_stack_client"])
-def compat_client(request, client_with_models):
-    if request.param == "openai_client" and isinstance(client_with_models, LlamaStackAsLibraryClient):
-        pytest.skip("OpenAI client tests not supported with library client")
-    return request.getfixturevalue(request.param)
-
-
 @pytest.fixture(scope="session")
 def sample_chunks():
     return [