Fixes and tying up of loose ends
- Handle ECT-CE event: issue a loss event.
- Log the fact that we ignore SETTINGS_MAX_HEADER_LIST_SIZE.
- Use Max Push ID in GOAWAY frame to cancel promises.
- Add support for HTTP/3 CANCEL_PUSH frame.
- lsquic_stream_is_pushed: streams without headers are never pushed.
- [BUGFIX] Regression in lsquic_stream_shutdown_internal: now it shuts down.
- Improve logic whether to generate CONNECTION_CLOSE.