Implements Tunnel type that listens on a local port, accepts WinBox client
connections, dials the remote RouterOS device, and proxies traffic
bidirectionally. Uses activityReader to atomically update LastActive on
each read for idle timeout detection. Per-connection contexts derive from
the tunnel context so Close() terminates all connections cleanly.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
