Why not use getaddrinfo_a / getaddrinfo_async_start / GetAddrInfoExW?

Or just use some standalone DNS resolve code or library (which basically replicates getaddrinfo but supports this in an async way)?

See also here the discussion: https://github.com/crystal-lang/crystal/issues/13619

A standalone library would have to work with all the existing system facilities (e.g. NSS on Linux systems) to be not restricted to just resolv.conf entries, but to allow for all the various other methods of resolving names.