Expose exact per-response usage in raw app-server events (#32985)

## Why

Clients that account for individual upstream Responses API calls need the exact
usage for each completion rather than accumulated or estimated thread usage.

## What changed

- Add the opt-in `rawResponse/completed` app-server notification with the
  `threadId`, `turnId`, `responseId`, and upstream `usage` payload.
- Emit the transient event for normal turns and compaction requests when
  `experimentalRawEvents` is enabled. The event is not persisted or replayed,
  and `usage` is `null` when the upstream response omits it.
- Export the notification in the app-server schemas and document its behavior.

## Testing

- Cover exact token breakdowns for turn and compaction completions.

GitOrigin-RevId: 49040a060bf1784c1ff1dd62112efb4a778428c4

codex-rs/mcp-server/src/codex_tool_runner.rs

@@ -358,6 +358,7 @@ async fn run_codex_tool_session_inner(
                     | EventMsg::ImageGenerationEnd(_)
                     | EventMsg::ViewImageToolCall(_)
                     | EventMsg::RawResponseItem(_)
+                    | EventMsg::RawResponseCompleted(_)
                     | EventMsg::EnteredReviewMode(_)
                     | EventMsg::ItemStarted(_)
                     | EventMsg::ItemCompleted(_)