feat: add static embedding metadata to dynamic model listings for providers using OpenAIMixin (#3547)

# What does this PR do?

- remove auto-download of ollama embedding models
- add embedding model metadata to dynamic listing w/ unit test
- add support and tests for allowed_models
- removed inference provider models.py files where dynamic listing is
enabled
- store embedding metadata in embedding_model_metadata field on
inference providers
- make model_entries optional on ModelRegistryHelper and
LiteLLMOpenAIMixin
- make OpenAIMixin a ModelRegistryHelper
- skip base64 embedding test for remote::ollama, always returns floats
- only use OpenAI client for ollama model listing
- remove unused build_model_entry function
- remove unused get_huggingface_repo function


## Test Plan

ci w/ new tests

llama_stack/providers/remote/inference/sambanova/models.py

@@ -1,28 +0,0 @@
-# Copyright (c) Meta Platforms, Inc. and affiliates.
-# All rights reserved.
-#
-# This source code is licensed under the terms described in the LICENSE file in
-# the root directory of this source tree.
-
-from llama_stack.models.llama.sku_types import CoreModelId
-from llama_stack.providers.utils.inference.model_registry import (
-    build_hf_repo_model_entry,
-)
-
-SAFETY_MODELS_ENTRIES = []
-
-
-MODEL_ENTRIES = [
-    build_hf_repo_model_entry(
-        "Meta-Llama-3.1-8B-Instruct",
-        CoreModelId.llama3_1_8b_instruct.value,
-    ),
-    build_hf_repo_model_entry(
-        "Meta-Llama-3.3-70B-Instruct",
-        CoreModelId.llama3_3_70b_instruct.value,
-    ),
-    build_hf_repo_model_entry(
-        "Llama-4-Maverick-17B-128E-Instruct",
-        CoreModelId.llama4_maverick_17b_128e_instruct.value,
-    ),
-] + SAFETY_MODELS_ENTRIES

llama_stack/providers/remote/inference/sambanova/sambanova.py

@@ -9,7 +9,6 @@ from llama_stack.providers.utils.inference.litellm_openai_mixin import LiteLLMOp
 from llama_stack.providers.utils.inference.openai_mixin import OpenAIMixin
 
 from .config import SambaNovaImplConfig
-from .models import MODEL_ENTRIES
 
 
 class SambaNovaInferenceAdapter(OpenAIMixin, LiteLLMOpenAIMixin):
@@ -29,7 +28,6 @@ class SambaNovaInferenceAdapter(OpenAIMixin, LiteLLMOpenAIMixin):
         self.environment_available_models = []
         LiteLLMOpenAIMixin.__init__(
             self,
-            model_entries=MODEL_ENTRIES,
             litellm_provider_name="sambanova",
             api_key_from_config=self.config.api_key.get_secret_value() if self.config.api_key else None,
             provider_data_api_key_field="sambanova_api_key",