feat(netxlite): implements NS queries (#734)

This diff has been extracted from eb0bf38957.

See https://github.com/ooni/probe/issues/2096.

While there, skip the broken tests caused by issue
https://github.com/ooni/probe/issues/2098.

internal/model/mocks/dnsdecoder_test.go

@@ -2,6 +2,7 @@ package mocks
 
 import (
 	"errors"
+	"net"
 	"testing"
 
 	"github.com/miekg/dns"
@@ -41,6 +42,22 @@ func TestDNSDecoder(t *testing.T) {
 		}
 	})
 
+	t.Run("DecodeNS", func(t *testing.T) {
+		expected := errors.New("mocked error")
+		e := &DNSDecoder{
+			MockDecodeNS: func(reply []byte, queryID uint16) ([]*net.NS, error) {
+				return nil, expected
+			},
+		}
+		out, err := e.DecodeNS(make([]byte, 17), dns.Id())
+		if !errors.Is(err, expected) {
+			t.Fatal("unexpected err", err)
+		}
+		if out != nil {
+			t.Fatal("unexpected out")
+		}
+	})
+
 	t.Run("DecodeReply", func(t *testing.T) {
 		expected := errors.New("mocked error")
 		e := &DNSDecoder{