## What changed
- Add `Client::get_thread_usage` for querying authoritative estimated credit
and dollar usage for a thread across both supported backend path styles.
- Expose usage totals and optional model, reasoning effort, speed, and token
breakdowns through `ThreadUsage` and `ThreadUsageBreakdownGroup`.
- Reject responses that do not include the requested thread.
## Testing
- Cover endpoint paths, request serialization, complete and partial usage
responses, and mismatched thread IDs.
GitOrigin-RevId: 16c83590b2c804e0182b4493cf2aa39206029c77
