add support for Known Answer Suppression part 1

[keepsimple1]

This is to resolve issue #193 item 1 (i.e. RFC 6762 section 7.1 Known Answer Suppression)

• Added clone_box() to DnsRecordExt to support clone.
• Added a new test case for Known Answer Suppression (but more tests are needed to have full coverage).

Also ran test with debug message to confirm: [2024-06-16T04:30:13Z DEBUG mdns_sd::service_daemon] Sending query questions: [("_known-answer._udp.local.", 12)] [2024-06-16T04:30:13Z DEBUG mdns_sd::service_daemon] add known answer: DnsPointer { record: DnsRecord { entry: DnsEntry { name: "_known-answer._udp.local.", ty: 12, class: 1, cache_flush: false }, ttl: 4500, created: 1718512213174, expires: 1718516713174, refresh: 1718515813174 }, alias: "1718512213167281._known-answer._udp.local." }