- 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
