std.Io.Threaded: OpenBSD implementation of `netLookup`

[andrewrk]

Extracted from #25592.

The OpenBSD implementation of netLookup should use getaddrinfo_async / asr_abort to obtain these two properties:

• asynchronously add to results queue
• cancellation integration

    if (native_os == .openbsd) {
        // TODO use getaddrinfo_async / asr_abort
    }