Gateway Discovery

LAN instrument discovery

LAN discovery of SCPI instruments: TCP port scan + *IDN? probe.

FastAPI-free (stdlib + scpi_control only; Python 3.8-clean), mirroring sessions.py. The scan runs on the caller's thread; instrument session worker threads are never involved. Callers must pass already-held addresses in skip — Siglent raw sockets allow one client, so probing a live session's instrument could disturb it.