Pure-Rust userspace network proxy for libkrun on macOS.
Uses a Unix datagram socketpair() to connect libkrun's virtio-net backend
to the userspace gateway and provides the gateway services needed by the guest:
- ARP: handled automatically by smoltcp's interface layer.
- DNS: UDP/53 queries forwarded to the host's configured DNS servers.
- Inbound TCP port-forwarding:
host_port → guest_ip:guest_portpairs parsed from the box'sport_mapconfig (e.g."8088:80").
General outbound NAT (VM → internet) is not provided by bridge mode yet.