Add support for the `ip6zone` protocol

Description

libp2p should support Multiaddrs with the ip6zone protocol. For example, a Multiaddr like this should be supported:

/ip6/fe80::9700:803e:ca65:66e8:c21/ip6zone/wlan0/udp/12345/quic-v1

Motivation

This would enable usage of libp2p on local networks without any IP address assignment by utilizing the link-local addresses of the peers. Currently, this isn't possible, because the unix socket API requires the scope_id of a socket_addr to be set to the index of the network interface which should be used to talk to link-local IP addresses, but no libp2p transport supports this.

Requirements

Each transport that connects to unix sockets using an IPv6 address that it got from a Multiaddr (this includes at least the quic, tcp, and webrtc transports), should additionally check, if this Multiaddr also defines a zone name using the ip6zone protocol, and – if it does – should use this zone name to populate the scope_id of the socket_addr before connecting.

Open questions

No response

Are you planning to do it yourself in a pull request ?

Yes

Trace how the Multiaddr is converted into a socket_addr in the quic, tcp, and webrtc transports, focusing on IPv6 connection paths. Verify how an ip6zone value can populate scope_id, then test that each affected transport connects using the zone from the example Multiaddr.