refactor: interfaces and data types into the model package (#642)

## Checklist

- [x] I have read the [contribution guidelines](https://github.com/ooni/probe-cli/blob/master/CONTRIBUTING.md)
- [x] reference issue for this pull request: https://github.com/ooni/probe/issues/1885
- [x] related ooni/spec pull request: N/A

Location of the issue tracker: https://github.com/ooni/probe

## Description

This PR contains a set of changes to move important interfaces and data types into the `./internal/model` package.

The criteria for including an interface or data type in here is roughly that the type should be important and used by several packages. We are especially interested to move more interfaces here to increase modularity.

An additional side effect is that, by reading this package, one should be able to understand more quickly how different parts of the codebase interact with each other.

This is what I want to move in `internal/model`:

- [x] most important interfaces from `internal/netxlite`
- [x] everything that was previously part of `internal/engine/model`
- [x] mocks from `internal/netxlite/mocks` should also be moved in here as a subpackage

internal/engine/experiment/webconnectivity/connects.go

@@ -6,7 +6,7 @@ import (
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
-	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
 // ConnectsConfig contains the config for Connects

internal/engine/experiment/webconnectivity/control.go

@@ -6,7 +6,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/engine/geolocate"
 	"github.com/ooni/probe-cli/v3/internal/engine/httpx"
 	legacyerrorsx "github.com/ooni/probe-cli/v3/internal/engine/legacy/errorsx"
-	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 )
 

internal/engine/experiment/webconnectivity/dnslookup.go

@@ -8,7 +8,7 @@ import (
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
-	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
 // DNSLookupConfig contains settings for the DNS lookup.

internal/engine/experiment/webconnectivity/httpanalysis.go

@@ -7,7 +7,7 @@ import (
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity/internal"
-	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
 // HTTPAnalysisResult contains the results of the analysis performed on the

internal/engine/experiment/webconnectivity/httpget.go

@@ -9,7 +9,7 @@ import (
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/urlgetter"
-	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
 // HTTPGetConfig contains the config for HTTPGet

internal/engine/experiment/webconnectivity/summary.go

@@ -4,7 +4,7 @@ import (
 	"strings"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity/internal"
-	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 )
 

internal/engine/experiment/webconnectivity/webconnectivity.go

@@ -13,8 +13,8 @@ import (
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity/internal"
 	"github.com/ooni/probe-cli/v3/internal/engine/httpheader"
-	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/archival"
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
 const (
@@ -149,7 +149,7 @@ func (m Measurer) Run(
 	}
 	// 1. find test helper
 	testhelpers, _ := sess.GetTestHelpersByName("web-connectivity")
-	var testhelper *model.Service
+	var testhelper *model.OOAPIService
 	for _, th := range testhelpers {
 		if th.Type == "https" {
 			testhelper = &th

internal/engine/experiment/webconnectivity/webconnectivity_test.go

@@ -11,8 +11,8 @@ import (
 	"github.com/google/go-cmp/cmp"
 	engine "github.com/ooni/probe-cli/v3/internal/engine"
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity"
-	"github.com/ooni/probe-cli/v3/internal/engine/model"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/archival"
+	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 )
 
@@ -202,7 +202,7 @@ func TestMeasureWithNoAvailableTestHelpers(t *testing.T) {
 
 func newsession(t *testing.T, lookupBackends bool) model.ExperimentSession {
 	sess, err := engine.NewSession(context.Background(), engine.SessionConfig{
-		AvailableProbeServices: []model.Service{{
+		AvailableProbeServices: []model.OOAPIService{{
 			Address: "https://ams-pg-test.ooni.org",
 			Type:    "https",
 		}},