The ErrNotImplemented sentinel error was dead code left over from
initial scaffolding. The resolver performs real iterative DNS
lookups from root servers, PortCheck does TCP connection checks,
and TLSCheck verifies TLS certificates and expiry. Removed the
unused error constant.
35 tests define the full resolver contract using live DNS queries
against *.dns.sneak.cloud (Cloudflare). Tests cover:
- FindAuthoritativeNameservers: iterative NS discovery, sorting,
determinism, trailing dot handling, TLD and subdomain cases
- QueryNameserver: A, AAAA, CNAME, MX, TXT, NXDOMAIN, per-NS
response model with status field, sorted record values
- QueryAllNameservers: independent per-NS queries, consistency
verification, NXDOMAIN from all NS
- LookupNS: NS record lookup matching FindAuthoritative
- ResolveIPAddresses: basic, multi-A, IPv6, dual-stack, CNAME
following, deduplication, sorting, NXDOMAIN returns empty
- Context cancellation for all methods
- Iterative resolution proof (resolves example.com from root)
Also adds DNSSEC validation to planned future features in README.
