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/inference/test_openai_completion.py

@@ -6,9 +6,6 @@
 
 
 import pytest
-from openai import OpenAI
-
-from llama_stack.core.library_client import LlamaStackAsLibraryClient
 
 from ..test_cases.test_case import TestCase
 
@@ -59,9 +56,6 @@ def skip_if_model_doesnt_support_suffix(client_with_models, model_id):
 
 
 def skip_if_model_doesnt_support_openai_chat_completion(client_with_models, model_id):
-    if isinstance(client_with_models, LlamaStackAsLibraryClient):
-        pytest.skip("OpenAI chat completions are not supported when testing with library client yet.")
-
     provider = provider_from_model(client_with_models, model_id)
     if provider.provider_type in (
         "inline::meta-reference",
@@ -90,17 +84,6 @@ def skip_if_provider_isnt_openai(client_with_models, model_id):
         )
 
 
-@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="bar")
-
-
-@pytest.fixture(params=["openai_client", "llama_stack_client"])
-def compat_client(request):
-    return request.getfixturevalue(request.param)
-
-
 @pytest.mark.parametrize(
     "test_case",
     [