[pull] main from openai:main - #129

…ate websocket events (#3617)

## Summary

- Add GPT-5.5 dated and Pro model identifiers, the `ultrafast` Responses
service tier, and optional model shutdown dates, including support in
the handwritten Responses streaming and parsing helpers.
- Represent MCP tool-call failures with one reusable, discriminated
structured error model covering protocol, tool-execution, and HTTP
errors. Remove the previously advertised string variant because the API
neither returns nor accepts it.
- Correct Responses WebSocket error events to expose their actual nested
error payload, status, headers, sequence numbers, and stream IDs.
- Add typed output-text annotations, cache-only web-search controls, and
text/image completion-token usage; clarify completed reasoning-item
reuse and file-content responses.

Co-authored-by: apcha-oai <228803254+apcha-oai@users.noreply.github.com>