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/gemini/gemini.py

@@ -8,14 +8,16 @@ from llama_stack.providers.utils.inference.litellm_openai_mixin import LiteLLMOp
 from llama_stack.providers.utils.inference.openai_mixin import OpenAIMixin
 
 from .config import GeminiConfig
-from .models import MODEL_ENTRIES
 
 
 class GeminiInferenceAdapter(OpenAIMixin, LiteLLMOpenAIMixin):
+    embedding_model_metadata = {
+        "text-embedding-004": {"embedding_dimension": 768, "context_length": 2048},
+    }
+
     def __init__(self, config: GeminiConfig) -> None:
         LiteLLMOpenAIMixin.__init__(
             self,
-            MODEL_ENTRIES,
             litellm_provider_name="gemini",
             api_key_from_config=config.api_key,
             provider_data_api_key_field="gemini_api_key",

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

@@ -1,34 +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.apis.models import ModelType
-from llama_stack.providers.utils.inference.model_registry import (
-    ProviderModelEntry,
-)
-
-LLM_MODEL_IDS = [
-    "gemini-1.5-flash",
-    "gemini-1.5-pro",
-    "gemini-2.0-flash",
-    "gemini-2.0-flash-lite",
-    "gemini-2.5-flash",
-    "gemini-2.5-flash-lite",
-    "gemini-2.5-pro",
-]
-
-SAFETY_MODELS_ENTRIES = []
-
-MODEL_ENTRIES = (
-    [ProviderModelEntry(provider_model_id=m) for m in LLM_MODEL_IDS]
-    + [
-        ProviderModelEntry(
-            provider_model_id="text-embedding-004",
-            model_type=ModelType.embedding,
-            metadata={"embedding_dimension": 768, "context_length": 2048},
-        ),
-    ]
-    + SAFETY_MODELS_ENTRIES
-)