dns: stream results from the resolver as they occur.

Description:
Currently the interaction between the DNS resolver (both implementations) and the callback target is state of the world i.e., resolved addresses are only returned once the resolution is complete, not as addresses become available.

This is specially pronounced in the All mode where the resolver waits for both family addresses to resolve before returning. Additionally in the Apple resolver the Apple API would allow for further streaming as it itself is a streaming API where a callback is fired per address resolved. Meaning that in the Apple resolver case those addresses could in turn also be streamed to the resolver's target.