fix(dns-scanner): extended CNAME/NS results

[lcampbell2]

• Updated dns_scanner.py to:

  • include CNAME in the record_exists gate (alongside A, SOA, NS),
  • preserve/derive rcode from multiple query attempts more reliably,
  • add new result fields:
    • ns_delegations
    • registrar_context
  • call new helper functions for NS delegation checks and RDAP registrar context.

• Added new module ns_registrar.py with:

  • check_ns_delegations(...)
    • resolves NS hosts,
    • probes authoritative SOA responses directly against nameserver IPs,
    • classifies delegation health as none / partial / full lame delegation.
  • get_registrar_context(...)
    • performs RDAP lookup via https://rdap.org/domain/<domain>,
    • extracts registrar metadata and RDAP nameservers,
    • compares observed delegation NS hosts with RDAP NS data.

[FestiveKyle]

I'm having trouble getting this to flag a real lame nameserver, do you have a working domain I can test it against?