feat: dnsping using step-by-step (#831)

Reference issue for this pull request: https://github.com/ooni/probe/issues/2159

This diff refactors the `dnsping` experiment to use the [step-by-step measurement style](https://github.com/ooni/probe-cli/blob/master/docs/design/dd-003-step-by-step.md).

Co-authored-by: decfox <decfox@github.com>
Co-authored-by: Simone Basso <bassosimone@gmail.com>

internal/tutorial/netxlite/chapter06/main.go

@@ -54,7 +54,7 @@ func main() {
 	// UDP endpoint address at which the server is listening.
 	//
 	// ```Go
-	reso := netxlite.NewParallelResolverUDP(log.Log, dialer, *serverAddr)
+	reso := netxlite.NewParallelUDPResolver(log.Log, dialer, *serverAddr)
 	// ```
 	//
 	// The API we invoke is the same as in the previous chapter, though,