UDP listener that registers bound endpoints in ListenRegistry.
What problem this solves
SO_REUSEPORT spreads UDP receives across shards, but RFC 5780 needs a stable
{transport, socket} for alternate-source Binding replies. This wrapper starts
DatagramServer and registers {ip, port} on boot so DualIp.reply_from/3
can resolve the correct shard.
Internal note
Used as the child module for UDP listeners in Supervisor; not configured directly.
RFCs
Summary
Functions
Starts DatagramServer and registers {ip, port} in ListenRegistry.