`void resp.body?.cancel()` in streamChatEvents' finally floated a
rejected promise: an aborted fetch errors the body with the abort
reason, and cancel() on an errored stream rejects with it, escaping
as unhandledRejection -> uncaughtException and killing pi on Escape.
Await the cancel inside the existing try/catch so the rejection is
actually swallowed. Adds a regression test that aborts a mocked
in-flight stream and asserts no unhandled rejection is raised.
Generated with [Devin](https://devin.ai)
Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
