refactor(engine): allow scripts to register experiments (#860)

See https://github.com/ooni/probe/issues/2216

cmd/ooniprobe/internal/nettests/dnscheck.go

@@ -16,7 +16,7 @@ func (n DNSCheck) lookupURLs(ctl *Controller) ([]string, error) {
 			// not needed because we have default static input in the engine
 		},
 		ExperimentName: "dnscheck",
-		InputPolicy:    engine.InputOrStaticDefault,
+		InputPolicy:    model.InputOrStaticDefault,
 		Session:        ctl.Session,
 		SourceFiles:    ctl.InputFiles,
 		StaticInputs:   ctl.Inputs,

cmd/ooniprobe/internal/nettests/nettests.go

@@ -123,7 +123,7 @@ func (c *Controller) SetNettestIndex(i, n int) {
 //
 // This function will continue to run in most cases but will
 // immediately halt if something's wrong with the file system.
-func (c *Controller) Run(builder engine.ExperimentBuilder, inputs []string) error {
+func (c *Controller) Run(builder model.ExperimentBuilder, inputs []string) error {
 	// This will configure the controller as handler for the callbacks
 	// called by ooni/probe-engine/experiment.Experiment.
 	builder.SetCallbacks(model.ExperimentCallbacks(c))

cmd/ooniprobe/internal/nettests/stunreachability.go

@@ -16,7 +16,7 @@ func (n STUNReachability) lookupURLs(ctl *Controller) ([]string, error) {
 			// not needed because we have default static input in the engine
 		},
 		ExperimentName: "stunreachability",
-		InputPolicy:    engine.InputOrStaticDefault,
+		InputPolicy:    model.InputOrStaticDefault,
 		Session:        ctl.Session,
 		SourceFiles:    ctl.InputFiles,
 		StaticInputs:   ctl.Inputs,

cmd/ooniprobe/internal/nettests/web_connectivity.go

@@ -22,7 +22,7 @@ func (n WebConnectivity) lookupURLs(ctl *Controller, categories []string) ([]str
 			},
 		},
 		ExperimentName: "web_connectivity",
-		InputPolicy:    engine.InputOrQueryBackend,
+		InputPolicy:    model.InputOrQueryBackend,
 		Session:        ctl.Session,
 		SourceFiles:    ctl.InputFiles,
 		StaticInputs:   ctl.Inputs,