feat(responses): implement usage tracking in streaming responses (#3771)

Implementats usage accumulation to StreamingResponseOrchestrator. 

The most important part was to pass `stream_options = { "include_usage":
true }` to the chat_completion call. This means I will have to record
all responses tests again because request hash will change :)

Test changes:
- Add usage assertions to streaming and non-streaming tests
- Update test recordings with actual usage data from OpenAI

llama_stack/providers/inline/agents/meta_reference/responses/streaming.py

@@ -39,12 +39,16 @@ from llama_stack.apis.agents.openai_responses import (
     OpenAIResponseOutputMessageFunctionToolCall,
     OpenAIResponseOutputMessageMCPListTools,
     OpenAIResponseText,
+    OpenAIResponseUsage,
+    OpenAIResponseUsageInputTokensDetails,
+    OpenAIResponseUsageOutputTokensDetails,
     WebSearchToolTypes,
 )
 from llama_stack.apis.inference import (
     Inference,
     OpenAIAssistantMessageParam,
     OpenAIChatCompletion,
+    OpenAIChatCompletionChunk,
     OpenAIChatCompletionToolCall,
     OpenAIChoice,
     OpenAIMessageParam,
@@ -104,6 +108,8 @@ class StreamingResponseOrchestrator:
         self.final_messages: list[OpenAIMessageParam] = []
         # mapping for annotations
         self.citation_files: dict[str, str] = {}
+        # Track accumulated usage across all inference calls
+        self.accumulated_usage: OpenAIResponseUsage | None = None
 
     def _clone_outputs(self, outputs: list[OpenAIResponseOutput]) -> list[OpenAIResponseOutput]:
         cloned: list[OpenAIResponseOutput] = []
@@ -131,6 +137,7 @@ class StreamingResponseOrchestrator:
             text=self.text,
             tools=self.ctx.available_tools(),
             error=error,
+            usage=self.accumulated_usage,
         )
 
     async def create_response(self) -> AsyncIterator[OpenAIResponseObjectStream]:
@@ -168,6 +175,9 @@ class StreamingResponseOrchestrator:
                     stream=True,
                     temperature=self.ctx.temperature,
                     response_format=response_format,
+                    stream_options={
+                        "include_usage": True,
+                    },
                 )
 
                 # Process streaming chunks and build complete response
@@ -298,6 +308,51 @@ class StreamingResponseOrchestrator:
 
         return function_tool_calls, non_function_tool_calls, approvals, next_turn_messages
 
+    def _accumulate_chunk_usage(self, chunk: OpenAIChatCompletionChunk) -> None:
+        """Accumulate usage from a streaming chunk into the response usage format."""
+        if not chunk.usage:
+            return
+
+        if self.accumulated_usage is None:
+            # Convert from chat completion format to response format
+            self.accumulated_usage = OpenAIResponseUsage(
+                input_tokens=chunk.usage.prompt_tokens,
+                output_tokens=chunk.usage.completion_tokens,
+                total_tokens=chunk.usage.total_tokens,
+                input_tokens_details=(
+                    OpenAIResponseUsageInputTokensDetails(cached_tokens=chunk.usage.prompt_tokens_details.cached_tokens)
+                    if chunk.usage.prompt_tokens_details
+                    else None
+                ),
+                output_tokens_details=(
+                    OpenAIResponseUsageOutputTokensDetails(
+                        reasoning_tokens=chunk.usage.completion_tokens_details.reasoning_tokens
+                    )
+                    if chunk.usage.completion_tokens_details
+                    else None
+                ),
+            )
+        else:
+            # Accumulate across multiple inference calls
+            self.accumulated_usage = OpenAIResponseUsage(
+                input_tokens=self.accumulated_usage.input_tokens + chunk.usage.prompt_tokens,
+                output_tokens=self.accumulated_usage.output_tokens + chunk.usage.completion_tokens,
+                total_tokens=self.accumulated_usage.total_tokens + chunk.usage.total_tokens,
+                # Use latest non-null details
+                input_tokens_details=(
+                    OpenAIResponseUsageInputTokensDetails(cached_tokens=chunk.usage.prompt_tokens_details.cached_tokens)
+                    if chunk.usage.prompt_tokens_details
+                    else self.accumulated_usage.input_tokens_details
+                ),
+                output_tokens_details=(
+                    OpenAIResponseUsageOutputTokensDetails(
+                        reasoning_tokens=chunk.usage.completion_tokens_details.reasoning_tokens
+                    )
+                    if chunk.usage.completion_tokens_details
+                    else self.accumulated_usage.output_tokens_details
+                ),
+            )
+
     async def _process_streaming_chunks(
         self, completion_result, output_messages: list[OpenAIResponseOutput]
     ) -> AsyncIterator[OpenAIResponseObjectStream | ChatCompletionResult]:
@@ -323,6 +378,10 @@ class StreamingResponseOrchestrator:
             chat_response_id = chunk.id
             chunk_created = chunk.created
             chunk_model = chunk.model
+
+            # Accumulate usage from chunks (typically in final chunk with stream_options)
+            self._accumulate_chunk_usage(chunk)
+
             for chunk_choice in chunk.choices:
                 # Emit incremental text content as delta events
                 if chunk_choice.delta.content: