feat: switch to new datum format

[agaffney]

Fixes #12

[agaffney]

Run server

$ ./chnsd 
{"level":"info","timestamp":"2023-07-21T14:06:16-05:00","caller":"chnsd/main.go:75","msg":"starting DNS listener on :8053"}
{"level":"info","timestamp":"2023-07-21T14:06:17-05:00","caller":"indexer/indexer.go:133","msg":"found updated registration for domain: snorkel.cardano."}
{"level":"info","timestamp":"2023-07-21T14:06:20-05:00","caller":"indexer/indexer.go:133","msg":"found updated registration for domain: dolphin.cardano."}

Perform queries

$ dig +short @localhost -p 8053 NS snorkel.cardano
ns1.snorkel.cardano.
ns2.snorkel.cardano.
$ dig +short @localhost -p 8053 A ns1.snorkel.cardano
0.0.0.0
$ dig +short @localhost -p 8053 A ns2.snorkel.cardano
42.42.31.31
$ dig +short @localhost -p 8053 NS dolphin.cardano
ns1.dolphin.cardano.
ns2.dolphin.cardano.
$ dig +short @localhost -p 8053 A ns1.dolphin.cardano
0.0.0.0
$ dig +short @localhost -p 8053 A ns2.dolphin.cardano
42.42.31.31