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/cerebras/cerebras.py

@@ -49,7 +49,6 @@ from llama_stack.providers.utils.inference.prompt_adapter import (
 )
 
 from .config import CerebrasImplConfig
-from .models import MODEL_ENTRIES
 
 
 class CerebrasInferenceAdapter(
@@ -58,10 +57,6 @@ class CerebrasInferenceAdapter(
     Inference,
 ):
     def __init__(self, config: CerebrasImplConfig) -> None:
-        ModelRegistryHelper.__init__(
-            self,
-            model_entries=MODEL_ENTRIES,
-        )
         self.config = config
 
         # TODO: make this use provider data, etc. like other providers

llama_stack/providers/remote/inference/cerebras/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 = []
-
-# https://inference-docs.cerebras.ai/models
-MODEL_ENTRIES = [
-    build_hf_repo_model_entry(
-        "llama3.1-8b",
-        CoreModelId.llama3_1_8b_instruct.value,
-    ),
-    build_hf_repo_model_entry(
-        "llama-3.3-70b",
-        CoreModelId.llama3_3_70b_instruct.value,
-    ),
-    build_hf_repo_model_entry(
-        "llama-4-scout-17b-16e-instruct",
-        CoreModelId.llama4_scout_17b_16e_instruct.value,
-    ),
-] + SAFETY_MODELS_ENTRIES