feat(netxlite): implement LookupHTTPS (#514)

This new API call performs DNS lookups for HTTPS records.

Part of https://github.com/ooni/probe/issues/1733 and diff has been
extracted from https://github.com/ooni/probe-cli/pull/506.

internal/netxlite/mocks/resolver.go

@@ -1,6 +1,10 @@
 package mocks
 
-import "context"
+import (
+	"context"
+
+	"github.com/ooni/probe-cli/v3/internal/netxlite/dnsx/model"
+)
 
 // Resolver is a mockable Resolver.
 type Resolver struct {
@@ -8,6 +12,7 @@ type Resolver struct {
 	MockNetwork              func() string
 	MockAddress              func() string
 	MockCloseIdleConnections func()
+	MockLookupHTTPS          func(ctx context.Context, domain string) (*HTTPSSvc, error)
 }
 
 // LookupHost calls MockLookupHost.
@@ -29,3 +34,11 @@ func (r *Resolver) Network() string {
 func (r *Resolver) CloseIdleConnections() {
 	r.MockCloseIdleConnections()
 }
+
+// HTTPSSvc is an HTTPSSvc reply.
+type HTTPSSvc = model.HTTPSSvc
+
+// LookupHTTPS calls MockLookupHTTPS.
+func (r *Resolver) LookupHTTPS(ctx context.Context, domain string) (*HTTPSSvc, error) {
+	return r.MockLookupHTTPS(ctx, domain)
+}

internal/netxlite/mocks/resolver_test.go

@@ -58,4 +58,21 @@ func TestResolver(t *testing.T) {
 			t.Fatal("not called")
 		}
 	})
+
+	t.Run("LookupHTTPS", func(t *testing.T) {
+		expected := errors.New("mocked error")
+		r := &Resolver{
+			MockLookupHTTPS: func(ctx context.Context, domain string) (*HTTPSSvc, error) {
+				return nil, expected
+			},
+		}
+		ctx := context.Background()
+		https, err := r.LookupHTTPS(ctx, "dns.google")
+		if !errors.Is(err, expected) {
+			t.Fatal("unexpected error", err)
+		}
+		if https != nil {
+			t.Fatal("expected nil addr")
+		}
+	})
 }