feat: add api.llama provider, llama-guard-4 model (#2058)

This PR adds a llama-stack inference provider for `api.llama.com`, as
well as adds entries for Llama-Guard-4 and updated Prompt-Guard models.

llama_stack/providers/utils/inference/openai_compat.py

@@ -638,10 +638,13 @@ async def convert_message_to_openai_dict_new(
             )
             for tool in message.tool_calls
         ]
+        params = {}
+        if tool_calls:
+            params["tool_calls"] = tool_calls
         out = OpenAIChatCompletionAssistantMessage(
             role="assistant",
             content=await _convert_message_content(message.content),
-            tool_calls=tool_calls or None,
+            **params,
         )
     elif isinstance(message, ToolResponseMessage):
         out = OpenAIChatCompletionToolMessage(