feat: basic server functionality

[agaffney]

No description provided.

[agaffney]

$ ./chnsd 
{"level":"info","timestamp":"2023-07-06T16:09:33-05:00","caller":"chnsd/main.go:69","msg":"starting DNS listener on :8053"}
{"level":"info","timestamp":"2023-07-06T16:09:38-05:00","caller":"dns/dns.go:43","msg":"request: AAAA foo."}
{"level":"info","timestamp":"2023-07-06T16:09:40-05:00","caller":"dns/dns.go:43","msg":"request: A bar."}

$ dig @localhost -p 8053 AAAA foo

; <<>> DiG 9.18.12-0ubuntu0.22.04.2-Ubuntu <<>> @localhost -p 8053 AAAA foo
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 60606
;; flags: qr rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;foo.				IN	AAAA

;; ANSWER SECTION:
test.zone.		0	IN	TXT	"AAAA foo."

;; Query time: 0 msec
;; SERVER: 127.0.0.1#8053(localhost) (UDP)
;; WHEN: Thu Jul 06 16:09:38 CDT 2023
;; MSG SIZE  rcvd: 52

$ dig @localhost -p 8053 A bar

; <<>> DiG 9.18.12-0ubuntu0.22.04.2-Ubuntu <<>> @localhost -p 8053 A bar
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3146
;; flags: qr rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;bar.				IN	A

;; ANSWER SECTION:
test.zone.		0	IN	TXT	"A bar."

;; Query time: 0 msec
;; SERVER: 127.0.0.1#8053(localhost) (UDP)
;; WHEN: Thu Jul 06 16:09:40 CDT 2023
;; MSG SIZE  rcvd: 49

[wolf31o2]

Approved, but with one question.