Update faulthandler to 3.14.2 by youknowone · Pull Request #6949 · RustPython/RustPython

- Rewrite faulthandler with live frame walking via
  Frame.previous AtomicPtr chain and thread-local
  CURRENT_FRAME (AtomicPtr) instead of frame snapshots
- Add signal-safe traceback dumping (dump_live_frames,
  dump_frame_from_raw) walking the Frame.previous chain
- Add safe_truncate/dump_ascii for UTF-8 safe string
  truncation in signal handlers
- Refactor write_thread_id to accept thread_id parameter
- Add SA_RESTART for user signal registration, SA_NODEFER
  only when chaining
- Save/restore errno in faulthandler_user_signal
- Add signal re-entrancy guard in trigger_signals to
  prevent recursive handler invocation
- Add thread frame tracking (push/pop/cleanup/reinit)
  with force_unlock fallback for post-fork recovery
- Remove expectedFailure markers for now-passing tests