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

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

internal/engine/experiment/sniblocking/sniblocking.go

@@ -233,12 +233,10 @@ func maybeURLToSNI(input model.MeasurementTarget) (model.MeasurementTarget, erro
 }
 
 // Run implements ExperimentMeasurer.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 {
+	callbacks := args.Callbacks
+	measurement := args.Measurement
+	sess := args.Session
 	m.mu.Lock()
 	if m.cache == nil {
 		m.cache = make(map[string]Subresult)

internal/engine/experiment/sniblocking/sniblocking_test.go

@@ -116,12 +116,12 @@ func TestMeasurerMeasureNoMeasurementInput(t *testing.T) {
 	measurer := NewExperimentMeasurer(Config{
 		ControlSNI: "example.com",
 	})
-	err := measurer.Run(
-		context.Background(),
-		newsession(),
-		new(model.Measurement),
-		model.NewPrinterCallbacks(log.Log),
-	)
+	args := &model.ExperimentArgs{
+		Callbacks:   model.NewPrinterCallbacks(log.Log),
+		Measurement: &model.Measurement{},
+		Session:     newsession(),
+	}
+	err := measurer.Run(context.Background(), args)
 	if err.Error() != "Experiment requires measurement.Input" {
 		t.Fatal("not the error we expected")
 	}
@@ -136,12 +136,12 @@ func TestMeasurerMeasureWithInvalidInput(t *testing.T) {
 	measurement := &model.Measurement{
 		Input: "\t",
 	}
-	err := measurer.Run(
-		ctx,
-		newsession(),
-		measurement,
-		model.NewPrinterCallbacks(log.Log),
-	)
+	args := &model.ExperimentArgs{
+		Callbacks:   model.NewPrinterCallbacks(log.Log),
+		Measurement: measurement,
+		Session:     newsession(),
+	}
+	err := measurer.Run(ctx, args)
 	if err == nil {
 		t.Fatal("expected an error here")
 	}
@@ -156,12 +156,12 @@ func TestMeasurerMeasureWithCancelledContext(t *testing.T) {
 	measurement := &model.Measurement{
 		Input: "kernel.org",
 	}
-	err := measurer.Run(
-		ctx,
-		newsession(),
-		measurement,
-		model.NewPrinterCallbacks(log.Log),
-	)
+	args := &model.ExperimentArgs{
+		Callbacks:   model.NewPrinterCallbacks(log.Log),
+		Measurement: measurement,
+		Session:     newsession(),
+	}
+	err := measurer.Run(ctx, args)
 	if err != nil {
 		t.Fatal(err)
 	}