fix(streaming): satisfy type-discipline and strict ruff budgets

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

litellm/completion_extras/litellm_responses_transformation/transformation.py

@@ -1612,7 +1612,11 @@ class OpenAiResponsesToChatCompletionStreamIterator(BaseModelResponseIterator):
                 ],
                 usage=usage,
                 provider_specific_fields=dict(provider_metadata) or None,  # mutable-ok: field is typed dict
-                **({"service_tier": served_service_tier} if isinstance(served_service_tier, str) else {}),
+                **(
+                    MappingProxyType({"service_tier": served_service_tier})
+                    if isinstance(served_service_tier, str)
+                    else MappingProxyType({})
+                ),
             )
         else:
             pass

litellm/litellm_core_utils/streaming_chunk_builder_utils.py

@@ -408,7 +408,11 @@ class ChunkProcessor:
                 "created": created,
                 "model": model,
                 "system_fingerprint": system_fingerprint,
-                **({"service_tier": service_tier} if service_tier is not None else {}),
+                **(
+                    MappingProxyType({"service_tier": service_tier})
+                    if service_tier is not None
+                    else MappingProxyType({})
+                ),
                 "choices": [
                     {
                         "index": 0,

litellm/litellm_core_utils/streaming_handler.py

@@ -75,7 +75,7 @@ def _next_sync_or_exhausted(it: Any) -> object:
 def _stamp_served_service_tier(response: ModelResponseStream, complete_streaming_response: ModelResponse) -> None:
     served_tier: Final = complete_streaming_response.model_dump().get("service_tier")
     if isinstance(served_tier, str) and served_tier:
-        setattr(response, "service_tier", served_tier)
+        setattr(response, "service_tier", served_tier)  # noqa: B010  # pydantic extra, not a declared field
 
 
 def is_async_iterable(obj: object) -> bool: