refactor: pass experiment arguments using a struct (#983)

Closes https://github.com/ooni/probe/issues/2358.

internal/engine/experiment/urlgetter/urlgetter.go

@@ -97,10 +97,10 @@ func (m Measurer) ExperimentVersion() string {
 }
 
 // Run implements model.ExperimentSession.Run
-func (m Measurer) Run(
-	ctx context.Context, sess model.ExperimentSession,
-	measurement *model.Measurement, callbacks model.ExperimentCallbacks,
-) error {
+func (m Measurer) Run(ctx context.Context, args *model.ExperimentArgs) error {
+	_ = args.Callbacks
+	measurement := args.Measurement
+	sess := args.Session
 	// When using the urlgetter experiment directly, there is a nonconfigurable
 	// default timeout that applies. When urlgetter is used as a library, it's
 	// instead the responsibility of the user of urlgetter to set timeouts. Note

internal/engine/experiment/urlgetter/urlgetter_test.go

@@ -23,10 +23,12 @@ func TestMeasurer(t *testing.T) {
 	}
 	measurement := new(model.Measurement)
 	measurement.Input = "https://www.google.com"
-	err := m.Run(
-		ctx, &mockable.Session{},
-		measurement, model.NewPrinterCallbacks(log.Log),
-	)
+	args := &model.ExperimentArgs{
+		Callbacks:   model.NewPrinterCallbacks(log.Log),
+		Measurement: measurement,
+		Session:     &mockable.Session{},
+	}
+	err := m.Run(ctx, args)
 	if !errors.Is(err, nil) { // nil because we want to submit the measurement
 		t.Fatal("not the error we expected")
 	}
@@ -60,10 +62,12 @@ func TestMeasurerDNSCache(t *testing.T) {
 	}
 	measurement := new(model.Measurement)
 	measurement.Input = "https://www.google.com"
-	err := m.Run(
-		ctx, &mockable.Session{},
-		measurement, model.NewPrinterCallbacks(log.Log),
-	)
+	args := &model.ExperimentArgs{
+		Callbacks:   model.NewPrinterCallbacks(log.Log),
+		Measurement: measurement,
+		Session:     &mockable.Session{},
+	}
+	err := m.Run(ctx, args)
 	if !errors.Is(err, nil) { // nil because we want to submit the measurement
 		t.Fatal("not the error we expected")
 	}