fix: handle missing API keys gracefully in model refresh (#3493)

- Catch Errors from providers without API keys during model refresh
- Log as warning instead of exception to avoid a scary startup

Closes: #3492

Error message are now warnings instead of several tracebacks
```

INFO     2025-09-19 16:06:55,228 llama_stack.providers.utils.inference.inference_store:74 inference_store: Write queue disabled for SQLite to avoid   
         concurrency issues                                                                                                                           
WARNING  2025-09-19 16:06:59,362 llama_stack.providers.utils.inference.openai_mixin:327 providers::utils: Failed to list models for anthropic: API key
         is not set. Please provide a valid API key in the provider data header, e.g. x-llamastack-provider-data: {"anthropic_api_key": "<API_KEY>"}, 
         or in the provider config.                                                                                                                   
WARNING  2025-09-19 16:06:59,364 llama_stack.providers.utils.inference.openai_mixin:327 providers::utils: Failed to list models for gemini: API key is
         not set. Please provide a valid API key in the provider data header, e.g. x-llamastack-provider-data: {"gemini_api_key": "<API_KEY>"}, or in 
         the provider config.                                                                                                                         
WARNING  2025-09-19 16:06:59,367 llama_stack.providers.utils.inference.openai_mixin:327 providers::utils: Failed to list models for groq: API key is  
         not set. Please provide a valid API key in the provider data header, e.g. x-llamastack-provider-data: {"groq_api_key": "<API_KEY>"}, or in   
         the provider config.                                                                                                                         
WARNING  2025-09-19 16:06:59,372 llama_stack.providers.utils.inference.openai_mixin:327 providers::utils: Failed to list models for sambanova: API key
         is not set. Please provide a valid API key in the provider data header, e.g. x-llamastack-provider-data: {"sambanova_api_key": "<API_KEY>"}, 
         or in the provider config.                                                                                                                   
INFO     2025-09-19 16:06:59,533 llama_stack.core.utils.config_resolution:45 core: Using file path:                                                   

```

Signed-off-by: Derek Higgins <[email protected]>

Author: derekhiggins

llama_stack/core/routing_tables/models.py

@@ -33,7 +33,7 @@ async def refresh(self) -> None:
             try:
                 models = await provider.list_models()
             except Exception as e:
-                logger.exception(f"Model refresh failed for provider {provider_id}: {e}")
+                logger.warning(f"Model refresh failed for provider {provider_id}: {e}")
                 continue
 
             self.listed_providers.add(provider_id)