v0.1.13
- Metrics on shutdown: Added _flush_and_shutdown_metrics() and call it from stop_tracing() and atexit.
- Idempotent shutdown: _metrics_shutdown flag so the meter provider is only flushed/shut down once.
- No double shutdown: Atexit _cleanup() does nothing when _started is already False (so explicit stop_tracing() doesn’t get run again at exit).