feat(api): add compaction progress events (#3866)

## Summary

Adds typed compaction progress notifications to Responses streams and
WebSocket connections.

## Changes

- Expose response.compaction.compacting with its item ID, output index,
and sequence number
- Pass progress notifications through response stream helpers without
changing the accumulated response
- Recognize credit_balance_exhausted errors from managed agent turns

Co-authored-by: markstuart-oai <323302876+markstuart-oai@users.noreply.github.com>