test: skip model registration for unsupported providers (#1030)

# What does this PR do?
- Updated `test_register_with_llama_model` to skip tests when using the
Ollama provider, as it does not support custom model names.
- Delete `test_initialize_model_during_registering` since there is no
  "load_model" semantic that is exposed publicly on a provider.

These changes ensure that tests do not fail for providers with
incompatible behaviors.

Signed-off-by: Sébastien Han <seb@redhat.com>

[//]: # (If resolving an issue, uncomment and update the line below)
[//]: # (Closes #[issue-number])

## Test Plan

Run Ollama:

```
 uv run pytest -v -s -k "ollama" llama_stack/providers/tests/inference/test_model_registration.py
/Users/leseb/Documents/AI/llama-stack/.venv/lib/python3.13/site-packages/pytest_asyncio/plugin.py:207: PytestDeprecationWarning: The configuration option "asyncio_default_fixture_loop_scope" is unset.
The event loop scope for asynchronous fixtures will default to the fixture caching scope. Future versions of pytest-asyncio will default the loop scope for asynchronous fixtures to function scope. Set the default fixture loop scope explicitly in order to avoid unexpected behavior in the future. Valid fixture loop scopes are: "function", "class", "module", "package", "session"

  warnings.warn(PytestDeprecationWarning(_DEFAULT_FIXTURE_LOOP_SCOPE_UNSET))
========================================== test session starts ==========================================
platform darwin -- Python 3.13.1, pytest-8.3.4, pluggy-1.5.0 -- /Users/leseb/Documents/AI/llama-stack/.venv/bin/python3
cachedir: .pytest_cache
metadata: {'Python': '3.13.1', 'Platform': 'macOS-15.3-arm64-arm-64bit-Mach-O', 'Packages': {'pytest': '8.3.4', 'pluggy': '1.5.0'}, 'Plugins': {'html': '4.1.1', 'metadata': '3.1.1', 'asyncio': '0.25.3', 'anyio': '4.8.0', 'nbval': '0.11.0'}}
rootdir: /Users/leseb/Documents/AI/llama-stack
configfile: pyproject.toml
plugins: html-4.1.1, metadata-3.1.1, asyncio-0.25.3, anyio-4.8.0, nbval-0.11.0
asyncio: mode=Mode.STRICT, asyncio_default_fixture_loop_scope=None
collected 65 items / 60 deselected / 5 selected                                                         

llama_stack/providers/tests/inference/test_model_registration.py::TestModelRegistration::test_register_unsupported_model[-ollama] PASSED
llama_stack/providers/tests/inference/test_model_registration.py::TestModelRegistration::test_register_nonexistent_model[-ollama] PASSED
llama_stack/providers/tests/inference/test_model_registration.py::TestModelRegistration::test_register_with_llama_model[-ollama] SKIPPED
llama_stack/providers/tests/inference/test_model_registration.py::TestModelRegistration::test_register_with_invalid_llama_model[-ollama] PASSED

======================== 3 passed, 1 skipped, 60 deselected, 2 warnings in 0.22s ========================
```


[//]: # (## Documentation)
[//]: # (- [ ] Added a Changelog entry if the change is significant)

Signed-off-by: Sébastien Han <seb@redhat.com>

llama_stack/providers/tests/inference/test_model_registration.py

@@ -4,8 +4,6 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
-from unittest.mock import AsyncMock, patch
-
 import pytest
 
 # How to run this test:
@@ -15,6 +13,9 @@ import pytest
 
 
 class TestModelRegistration:
+    def provider_supports_custom_names(self, provider) -> bool:
+        return "remote::ollama" not in provider.__provider_spec__.provider_type
+
     @pytest.mark.asyncio
     async def test_register_unsupported_model(self, inference_stack, inference_model):
         inference_impl, models_impl = inference_stack
@@ -47,7 +48,12 @@ class TestModelRegistration:
             )
 
     @pytest.mark.asyncio
-    async def test_register_with_llama_model(self, inference_stack):
+    async def test_register_with_llama_model(self, inference_stack, inference_model):
+        inference_impl, models_impl = inference_stack
+        provider = inference_impl.routing_table.get_provider_impl(inference_model)
+        if not self.provider_supports_custom_names(provider):
+            pytest.skip("Provider does not support custom model names")
+
         _, models_impl = inference_stack
 
         _ = await models_impl.register_model(
@@ -67,22 +73,6 @@ class TestModelRegistration:
                 provider_model_id="custom-model",
             )
 
-    @pytest.mark.asyncio
-    async def test_initialize_model_during_registering(self, inference_stack):
-        _, models_impl = inference_stack
-
-        with patch(
-            "llama_stack.providers.inline.inference.meta_reference.inference.MetaReferenceInferenceImpl.load_model",
-            new_callable=AsyncMock,
-        ) as mock_load_model:
-            _ = await models_impl.register_model(
-                model_id="Llama3.1-8B-Instruct",
-                metadata={
-                    "llama_model": "meta-llama/Llama-3.1-8B-Instruct",
-                },
-            )
-            mock_load_model.assert_called_once()
-
     @pytest.mark.asyncio
     async def test_register_with_invalid_llama_model(self, inference_stack):
         _, models_impl = inference_stack