cleanup: remove unnecessary legacy interfaces (#656)

This diff addresses another point of https://github.com/ooni/probe/issues/1956:

> - [ ] observe that we're still using a bunch of private interfaces for common interfaces such as the `Dialer`, so we can get rid of these private interfaces and always use the ones in `model`, which allows us to remove a bunch of legacy wrappers

Additional cleanups may still be possible. The more I cleanup, the more I see
there's extra legacy code we can dispose of (which seems good?).

internal/cmd/oohelperd/internal/webconnectivity/dns.go

@@ -5,8 +5,8 @@ import (
 	"sync"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity"
-	"github.com/ooni/probe-cli/v3/internal/engine/netx"
 	"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"
 )
 
@@ -21,7 +21,7 @@ type CtrlDNSResult = webconnectivity.ControlDNSResult
 type DNSConfig struct {
 	Domain   string
 	Out      chan CtrlDNSResult
-	Resolver netx.Resolver
+	Resolver model.Resolver
 	Wg       *sync.WaitGroup
 }
 

internal/cmd/oohelperd/internal/webconnectivity/fake_test.go

@@ -2,13 +2,14 @@ package webconnectivity
 
 import (
 	"context"
+	"errors"
 	"io"
 	"net"
 	"net/http"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/atomicx"
-	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 )
 
@@ -49,7 +50,13 @@ func (c FakeResolver) Address() string {
 	return ""
 }
 
-var _ netx.Resolver = FakeResolver{}
+func (c FakeResolver) CloseIdleConnections() {}
+
+func (c FakeResolver) LookupHTTPS(ctx context.Context, domain string) (*model.HTTPSSvc, error) {
+	return nil, errors.New("not implemented")
+}
+
+var _ model.Resolver = FakeResolver{}
 
 type FakeTransport struct {
 	Err  error
@@ -75,7 +82,7 @@ func (txp FakeTransport) RoundTrip(req *http.Request) (*http.Response, error) {
 
 func (txp FakeTransport) CloseIdleConnections() {}
 
-var _ netx.HTTPRoundTripper = FakeTransport{}
+var _ model.HTTPTransport = FakeTransport{}
 
 type FakeBody struct {
 	Data []byte

internal/cmd/oohelperd/internal/webconnectivity/measure.go

@@ -8,7 +8,7 @@ import (
 	"sync"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity"
-	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
 type (
@@ -22,9 +22,9 @@ type (
 // MeasureConfig contains configuration for Measure.
 type MeasureConfig struct {
 	Client            *http.Client
-	Dialer            netx.Dialer
+	Dialer            model.Dialer
 	MaxAcceptableBody int64
-	Resolver          netx.Resolver
+	Resolver          model.Resolver
 }
 
 // Measure performs the measurement described by the request and

internal/cmd/oohelperd/internal/webconnectivity/tcpconnect.go

@@ -5,7 +5,7 @@ import (
 	"sync"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity"
-	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 )
 
@@ -20,7 +20,7 @@ type TCPResultPair struct {
 
 // TCPConfig configures the TCP connect check.
 type TCPConfig struct {
-	Dialer   netx.Dialer
+	Dialer   model.Dialer
 	Endpoint string
 	Out      chan TCPResultPair
 	Wg       *sync.WaitGroup

internal/cmd/oohelperd/internal/webconnectivity/webconnectivity.go

@@ -6,7 +6,7 @@ import (
 	"io"
 	"net/http"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 	"github.com/ooni/probe-cli/v3/internal/runtimex"
 	"github.com/ooni/probe-cli/v3/internal/version"
@@ -15,9 +15,9 @@ import (
 // Handler implements the Web Connectivity test helper HTTP API.
 type Handler struct {
 	Client            *http.Client
-	Dialer            netx.Dialer
+	Dialer            model.Dialer
 	MaxAcceptableBody int64
-	Resolver          netx.Resolver
+	Resolver          model.Resolver
 }
 
 func (h Handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {

internal/cmd/oohelperd/internal/webconnectivity/webconnectivity_test.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
-	"net"
 	"net/http"
 	"net/http/httptest"
 	"strings"
@@ -52,7 +51,7 @@ const requestWithoutDomainName = `{
 func TestWorkingAsIntended(t *testing.T) {
 	handler := Handler{
 		Client:            http.DefaultClient,
-		Dialer:            new(net.Dialer),
+		Dialer:            netxlite.DefaultDialer,
 		MaxAcceptableBody: 1 << 24,
 		Resolver:          &netxlite.ResolverSystem{},
 	}