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/agents/conftest.py

@@ -10,7 +10,7 @@ from ..conftest import get_provider_fixture_overrides
 
 from ..inference.fixtures import INFERENCE_FIXTURES
 from ..memory.fixtures import MEMORY_FIXTURES
-from ..safety.fixtures import SAFETY_FIXTURES
+from ..safety.fixtures import SAFETY_FIXTURES, safety_model_from_shield
 from .fixtures import AGENTS_FIXTURES
 
 
@@ -46,6 +46,16 @@ DEFAULT_PROVIDER_COMBINATIONS = [
         id="together",
         marks=pytest.mark.together,
     ),
+    pytest.param(
+        {
+            "inference": "fireworks",
+            "safety": "llama_guard",
+            "memory": "faiss",
+            "agents": "meta_reference",
+        },
+        id="fireworks",
+        marks=pytest.mark.fireworks,
+    ),
     pytest.param(
         {
             "inference": "remote",
@@ -60,7 +70,7 @@ DEFAULT_PROVIDER_COMBINATIONS = [
 
 
 def pytest_configure(config):
-    for mark in ["meta_reference", "ollama", "together", "remote"]:
+    for mark in ["meta_reference", "ollama", "together", "fireworks", "remote"]:
         config.addinivalue_line(
             "markers",
             f"{mark}: marks tests as {mark} specific",
@@ -75,28 +85,30 @@ def pytest_addoption(parser):
         help="Specify the inference model to use for testing",
     )
     parser.addoption(
-        "--safety-model",
+        "--safety-shield",
         action="store",
         default="Llama-Guard-3-8B",
-        help="Specify the safety model to use for testing",
+        help="Specify the safety shield to use for testing",
     )
 
 
 def pytest_generate_tests(metafunc):
-    safety_model = metafunc.config.getoption("--safety-model")
-    if "safety_model" in metafunc.fixturenames:
+    shield_id = metafunc.config.getoption("--safety-shield")
+    if "safety_shield" in metafunc.fixturenames:
         metafunc.parametrize(
-            "safety_model",
-            [pytest.param(safety_model, id="")],
+            "safety_shield",
+            [pytest.param(shield_id, id="")],
             indirect=True,
         )
     if "inference_model" in metafunc.fixturenames:
         inference_model = metafunc.config.getoption("--inference-model")
-        models = list(set({inference_model, safety_model}))
+        models = set({inference_model})
+        if safety_model := safety_model_from_shield(shield_id):
+            models.add(safety_model)
 
         metafunc.parametrize(
             "inference_model",
-            [pytest.param(models, id="")],
+            [pytest.param(list(models), id="")],
             indirect=True,
         )
     if "agents_stack" in metafunc.fixturenames: