- Closes#1268.
- The types we were using weren't very usable with Swift 6 structured
concurrency.
- Implements just the subset of records that we use.
- Use notImplemented instead of formatError for unknown record types.
- Use pure actor for LocalhostDNSHandler now that we have sendable
types.
- Use DNSName as key for table lookups in LocalhostDNSHandler and
HostTableResolver.
- Utilize dot-suffixed domain names everywhere in the lookup chain.
- Huge thanks to @manojmahapatra and @katiewasnothere for their
diligent and patient review :D