Observe the NS RRset TTL from each parent server (ParentView.NSTTL) and
whether each NS target name is a CNAME alias (ChildNSView.CNAMETarget).
Two new rules judge the collected facts:
- delegation_ns_ttl_inconsistent: warns when parent servers disagree on
the NS TTL, which indicates zone-data inconsistency between primaries.
- delegation_ns_is_cname: flags NS targets that are CNAME aliases as
critical, per RFC 2181 §10.3 which forbids aliased NS names.
