feat: clearly indicate which resolver we're using (#885)

See what we documented at https://github.com/ooni/spec/pull/257

Reference issue: https://github.com/ooni/probe/issues/2238

See also the related ooni/spec PR: https://github.com/ooni/spec/pull/257

See also https://github.com/ooni/probe/issues/2237

While there, bump webconnectivity@v0.5 version because this change
has an impact onto the generated data format.

The drop in coverage is unavoidable because we've written some
tests for `measurex` to ensure we deal with DNS resolvers and transport
names correctly depending on the splitting policy we use.

(However, `measurex` is only used for the `tor` experiment and, per
the step-by-step design document, new experiments should use
`measurexlite` instead, so this is hopefully fine(TM).)

While there, fix a broken integration test that does not run in `-short` mode.

internal/measurex/resolver_test.go

@@ -0,0 +1,58 @@
+package measurex
+
+import (
+	"context"
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/netxlite"
+)
+
+func TestResolverModifiesStdlibResolverName(t *testing.T) {
+	// See https://github.com/ooni/spec/pull/257 for more information.
+
+	t.Run("for LookupHost", func(t *testing.T) {
+		child := netxlite.NewStdlibResolver(model.DiscardLogger)
+		mx := NewMeasurerWithDefaultSettings()
+		dbout := &MeasurementDB{}
+		txp := mx.WrapResolver(dbout, child)
+		ctx, cancel := context.WithCancel(context.Background())
+		cancel() // we want to fail immediately
+		_, _ = txp.LookupHost(ctx, "dns.google")
+		measurement := dbout.AsMeasurement()
+		var good int
+		for _, rtinfo := range measurement.LookupHost {
+			network := rtinfo.Network
+			if network != netxlite.StdlibResolverSystem {
+				t.Fatal("unexpected network", network)
+			}
+			good++
+		}
+		if good < 1 {
+			t.Fatal("no good entry seen")
+		}
+	})
+
+	t.Run("for LookupHTTPS", func(t *testing.T) {
+		child := netxlite.NewStdlibResolver(model.DiscardLogger)
+		mx := NewMeasurerWithDefaultSettings()
+		dbout := &MeasurementDB{}
+		txp := mx.WrapResolver(dbout, child)
+		ctx, cancel := context.WithCancel(context.Background())
+		cancel() // we want to fail immediately
+		_, _ = txp.LookupHTTPS(ctx, "dns.google")
+		measurement := dbout.AsMeasurement()
+		var good int
+		for _, rtinfo := range measurement.LookupHTTPSSvc {
+			network := rtinfo.Network
+			if network != netxlite.StdlibResolverSystem {
+				t.Fatal("unexpected network", network)
+			}
+			good++
+		}
+		if good < 1 {
+			t.Fatal("no good entry seen")
+		}
+	})
+
+}