Kill "remote" providers and fix testing with a remote stack properly (#435)

# What does this PR do?

This PR kills the notion of "pure passthrough" remote providers. You
cannot specify a single provider you must specify a whole distribution
(stack) as remote.

This PR also significantly fixes / upgrades testing infrastructure so
you can now test against a remotely hosted stack server by just doing

```bash
pytest -s -v -m remote  test_agents.py \
  --inference-model=Llama3.1-8B-Instruct --safety-shield=Llama-Guard-3-1B \
  --env REMOTE_STACK_URL=http://localhost:5001
```

Also fixed `test_agents_persistence.py` (which was broken) and killed
some deprecated testing functions.

## Test Plan

All the tests.

llama_stack/providers/tests/safety/fixtures.py

@@ -16,7 +16,7 @@ from llama_stack.providers.inline.safety.llama_guard import LlamaGuardConfig
 from llama_stack.providers.inline.safety.prompt_guard import PromptGuardConfig
 from llama_stack.providers.remote.safety.bedrock import BedrockSafetyConfig
 
-from llama_stack.providers.tests.resolver import resolve_impls_for_test_v2
+from llama_stack.providers.tests.resolver import construct_stack_for_test
 
 from ..conftest import ProviderFixture, remote_stack_fixture
 from ..env import get_env_or_fail
@@ -27,19 +27,38 @@ def safety_remote() -> ProviderFixture:
     return remote_stack_fixture()
 
 
+def safety_model_from_shield(shield_id):
+    if shield_id in ("Bedrock", "CodeScanner", "CodeShield"):
+        return None
+
+    return shield_id
+
+
 @pytest.fixture(scope="session")
-def safety_model(request):
+def safety_shield(request):
     if hasattr(request, "param"):
-        return request.param
-    return request.config.getoption("--safety-model", None)
+        shield_id = request.param
+    else:
+        shield_id = request.config.getoption("--safety-shield", None)
+
+    if shield_id == "bedrock":
+        shield_id = get_env_or_fail("BEDROCK_GUARDRAIL_IDENTIFIER")
+        params = {"guardrailVersion": get_env_or_fail("BEDROCK_GUARDRAIL_VERSION")}
+    else:
+        params = {}
+
+    return ShieldInput(
+        shield_id=shield_id,
+        params=params,
+    )
 
 
 @pytest.fixture(scope="session")
-def safety_llama_guard(safety_model) -> ProviderFixture:
+def safety_llama_guard() -> ProviderFixture:
     return ProviderFixture(
         providers=[
             Provider(
-                provider_id="inline::llama-guard",
+                provider_id="llama-guard",
                 provider_type="inline::llama-guard",
                 config=LlamaGuardConfig().model_dump(),
             )
@@ -55,7 +74,7 @@ def safety_prompt_guard() -> ProviderFixture:
     return ProviderFixture(
         providers=[
             Provider(
-                provider_id="inline::prompt-guard",
+                provider_id="prompt-guard",
                 provider_type="inline::prompt-guard",
                 config=PromptGuardConfig().model_dump(),
             )
@@ -80,50 +99,25 @@ SAFETY_FIXTURES = ["llama_guard", "bedrock", "remote"]
 
 
 @pytest_asyncio.fixture(scope="session")
-async def safety_stack(inference_model, safety_model, request):
+async def safety_stack(inference_model, safety_shield, request):
     # We need an inference + safety fixture to test safety
     fixture_dict = request.param
-    inference_fixture = request.getfixturevalue(
-        f"inference_{fixture_dict['inference']}"
-    )
-    safety_fixture = request.getfixturevalue(f"safety_{fixture_dict['safety']}")
 
-    providers = {
-        "inference": inference_fixture.providers,
-        "safety": safety_fixture.providers,
-    }
+    providers = {}
     provider_data = {}
-    if inference_fixture.provider_data:
-        provider_data.update(inference_fixture.provider_data)
-    if safety_fixture.provider_data:
-        provider_data.update(safety_fixture.provider_data)
+    for key in ["inference", "safety"]:
+        fixture = request.getfixturevalue(f"{key}_{fixture_dict[key]}")
+        providers[key] = fixture.providers
+        if fixture.provider_data:
+            provider_data.update(fixture.provider_data)
 
-    shield_provider_type = safety_fixture.providers[0].provider_type
-    shield_input = get_shield_to_register(shield_provider_type, safety_model)
-
-    print(f"inference_model: {inference_model}")
-    print(f"shield_input = {shield_input}")
-    impls = await resolve_impls_for_test_v2(
+    test_stack = await construct_stack_for_test(
         [Api.safety, Api.shields, Api.inference],
         providers,
         provider_data,
         models=[ModelInput(model_id=inference_model)],
-        shields=[shield_input],
+        shields=[safety_shield],
     )
 
-    shield = await impls[Api.shields].get_shield(shield_input.shield_id)
-    return impls[Api.safety], impls[Api.shields], shield
-
-
-def get_shield_to_register(provider_type: str, safety_model: str) -> ShieldInput:
-    if provider_type == "remote::bedrock":
-        identifier = get_env_or_fail("BEDROCK_GUARDRAIL_IDENTIFIER")
-        params = {"guardrailVersion": get_env_or_fail("BEDROCK_GUARDRAIL_VERSION")}
-    else:
-        params = {}
-        identifier = safety_model
-
-    return ShieldInput(
-        shield_id=identifier,
-        params=params,
-    )
+    shield = await test_stack.impls[Api.shields].get_shield(safety_shield.shield_id)
+    return test_stack.impls[Api.safety], test_stack.impls[Api.shields], shield