chore: turn OpenAIMixin into a pydantic.BaseModel (#3671)

# What does this PR do?

- implement get_api_key instead of relying on
LiteLLMOpenAIMixin.get_api_key
 - remove use of LiteLLMOpenAIMixin
 - add default initialize/shutdown methods to OpenAIMixin
 - remove __init__s to allow proper pydantic construction
- remove dead code from vllm adapter and associated / duplicate unit
tests
 - update vllm adapter to use openaimixin for model registration
 - remove ModelRegistryHelper from fireworks & together adapters
 - remove Inference from nvidia adapter
 - complete type hints on embedding_model_metadata
- allow extra fields on OpenAIMixin, for model_store, __provider_id__,
etc
 - new recordings for ollama
 - enhance the list models error handling
- update cerebras (remove cerebras-cloud-sdk) and anthropic (custom
model listing) inference adapters
 - parametrized test_inference_client_caching
- remove cerebras, databricks, fireworks, together from blanket mypy
exclude
 - removed unnecessary litellm deps

## Test Plan

ci

llama_stack/providers/remote/inference/groq/__init__.py

@@ -11,5 +11,5 @@ async def get_adapter_impl(config: GroqConfig, _deps):
     # import dynamically so the import is used only when it is needed
     from .groq import GroqInferenceAdapter
 
-    adapter = GroqInferenceAdapter(config)
+    adapter = GroqInferenceAdapter(config=config)
     return adapter

llama_stack/providers/remote/inference/groq/groq.py

@@ -6,30 +6,16 @@
 
 
 from llama_stack.providers.remote.inference.groq.config import GroqConfig
-from llama_stack.providers.utils.inference.litellm_openai_mixin import LiteLLMOpenAIMixin
 from llama_stack.providers.utils.inference.openai_mixin import OpenAIMixin
 
 
-class GroqInferenceAdapter(OpenAIMixin, LiteLLMOpenAIMixin):
-    _config: GroqConfig
+class GroqInferenceAdapter(OpenAIMixin):
+    config: GroqConfig
 
-    def __init__(self, config: GroqConfig):
-        LiteLLMOpenAIMixin.__init__(
-            self,
-            litellm_provider_name="groq",
-            api_key_from_config=config.api_key,
-            provider_data_api_key_field="groq_api_key",
-        )
-        self.config = config
+    provider_data_api_key_field: str = "groq_api_key"
 
-    # Delegate the client data handling get_api_key method to LiteLLMOpenAIMixin
-    get_api_key = LiteLLMOpenAIMixin.get_api_key
+    def get_api_key(self) -> str:
+        return self.config.api_key or ""
 
     def get_base_url(self) -> str:
         return f"{self.config.url}/openai/v1"
-
-    async def initialize(self):
-        await super().initialize()
-
-    async def shutdown(self):
-        await super().shutdown()