addressing: resolve dns, dns4, dns6 and dnsaddr multiaddrs

[adust09]

Spec

specs/addressing/README.md, IP and Name Resolution.

The addressing recommendation defines resolution for /dns, /dns4, /dns6, and /dnsaddr; only the name-based component is replaced while the encapsulated transport suffix is retained.

Current state

LibP2P.Multiaddr.Protocol parses and renders all four DNS components, but Transport.TCP.canDialTCP, multiaddrToHostPort, and tcpDial accept only literal /ip4/.../tcp/... and /ip6/.../tcp/... addresses. Thus syntactically supported DNS multiaddrs cannot be dialled.

Scope

• Resolve /dns through A and AAAA records, preferring IPv6 as specified while retaining usable fallbacks.
• Resolve /dns4 through A records only.
• Resolve /dns6 through AAAA records only.
• Resolve /dnsaddr through _dnsaddr.<name> TXT records and recursively parse the returned dnsaddr= multiaddrs.
• Preserve encapsulated suffixes such as /tcp/.../p2p/... during resolution.
• Bound recursion, result count, lookup time, and malformed TXT handling.
• Integrate resolution with Switch dialing without making the TCP transport falsely claim unsupported address shapes.

Acceptance tests

• Deterministic resolver tests for dns/dns4/dns6/dnsaddr.
• TCP dial through a name-based multiaddr using an injected/local resolver.
• Multiple answers fall back after a failed address.
• Recursive/cyclic dnsaddr records terminate safely.
• /p2p/<peer-id> suffix and peer identity verification survive resolution.