Enable Dual-Stack IPv4/IPv6 Support in Lighthouse Ethereum Client

IPv6 support in Ethereum lags despite internet-wide adoption. Lighthouse enables dual-stack IPv4/IPv6 listening by default on port 9000 TCP and UDP 9001. Configure with --listen-address 0.0.0.0 and ::, allow inbound IPv6 via firewall, and verify using netstat -ntlp6 or ip -6 addr. Check NAT status at localhost:5052/lighthouse/nat or Lighthouse logs. More IPv6 nodes ease network access.