fix: Together provider shutdown and default to non-streaming

The together inference provider was throwing a stack trace every time
it shut down, as it was trying to call a non-existent `close` method
on the AsyncTogether client. While fixing that, I also adjusted its
shutdown logic to close the OpenAI client if we've created one of
those, as that client does have a `close` method.

In testing that, I also realized we were defaulting to treating all
requests as streaming requests instead of defaulting to
non-streaming. So, this flips that default to non-streaming to match
how the other providers work.

I tested this by ensuring the together inference provider no longer
spits out a long stack trace when shutting it down and by running the
OpenAI API chat completion  verification suite to ensure the change in
default streaming logic didn't mess anything else up.

Signed-off-by: Ben Browning <bbrownin@redhat.com>

llama_stack/providers/remote/inference/together/together.py

@@ -76,8 +76,11 @@ class TogetherInferenceAdapter(ModelRegistryHelper, Inference, NeedsRequestProvi
 
     async def shutdown(self) -> None:
         if self._client:
-            await self._client.close()
+            # Together client has no close method, so just set to None
             self._client = None
+        if self._openai_client:
+            await self._openai_client.close()
+            self._openai_client = None
 
     async def completion(
         self,
@@ -359,7 +362,7 @@ class TogetherInferenceAdapter(ModelRegistryHelper, Inference, NeedsRequestProvi
             top_p=top_p,
             user=user,
         )
-        if params.get("stream", True):
+        if params.get("stream", False):
             return self._stream_openai_chat_completion(params)
         return await self._get_openai_client().chat.completions.create(**params)  # type: ignore