The DNS responder was setting RCODE=NXDOMAIN (Name Error) any time the
answer section was empty, including for names that exist in the
lighthouse but lack a record of the requested type (e.g. an AAAA query
for a v4-only host). Per RFC 2308 §2.1, NXDOMAIN means "the domain
referred to by the QNAME does not exist", and per RFC 2308 §2.2 a name
that exists with no record of the requested type must be answered with
RCODE=NOERROR and an empty answer section (NODATA).
The practical fallout: busybox ping in Alpine issues AAAA first, treats
NXDOMAIN as a hard failure, and never falls through to A. Returning
NODATA lets the resolver continue to the A query as it should.
Track whether any queried A/AAAA name is known in either map and only
set RcodeNameError when no queried name exists at all.
* upgrade to yaml.v3
The main nice fix here is that maps unmarshal into `map[string]any`
instead of `map[any]any`, so it cleans things up a bit.
* add config.AsBool
Since yaml.v3 doesn't automatically convert yes to bool now, for
backwards compat
* use type aliases for m
* more cleanup
* more cleanup
* more cleanup
* go mod cleanup
