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/engine/netx/quicdialer/quicdialer.go

@@ -1,20 +0,0 @@
-package quicdialer
-
-import (
-	"context"
-	"crypto/tls"
-
-	"github.com/lucas-clemente/quic-go"
-)
-
-// ContextDialer is a dialer for QUIC using Context.
-type ContextDialer interface {
-	// Note: assumes that tlsCfg and cfg are not nil.
-	DialContext(ctx context.Context, network, host string,
-		tlsCfg *tls.Config, cfg *quic.Config) (quic.EarlySession, error)
-}
-
-// Resolver is the interface we expect from a resolver.
-type Resolver interface {
-	LookupHost(ctx context.Context, hostname string) (addrs []string, err error)
-}

internal/engine/netx/quicdialer/saver.go

@@ -7,13 +7,14 @@ import (
 
 	"github.com/lucas-clemente/quic-go"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/trace"
+	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 )
 
 // HandshakeSaver saves events occurring during the handshake
 type HandshakeSaver struct {
-	Saver  *trace.Saver
-	Dialer ContextDialer
+	Saver *trace.Saver
+	model.QUICDialer
 }
 
 // DialContext implements ContextDialer.DialContext
@@ -31,7 +32,7 @@ func (h HandshakeSaver) DialContext(ctx context.Context, network string,
 		TLSServerName: tlsCfg.ServerName,
 		Time:          start,
 	})
-	sess, err := h.Dialer.DialContext(ctx, network, host, tlsCfg, cfg)
+	sess, err := h.QUICDialer.DialContext(ctx, network, host, tlsCfg, cfg)
 	stop := time.Now()
 	if err != nil {
 		h.Saver.Write(trace.Event{

internal/engine/netx/quicdialer/saver_test.go

@@ -11,12 +11,13 @@ import (
 	"github.com/lucas-clemente/quic-go"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/quicdialer"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/trace"
+	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 	"github.com/ooni/probe-cli/v3/internal/netxlite/quictesting"
 )
 
 type MockDialer struct {
-	Dialer quicdialer.ContextDialer
+	Dialer model.QUICDialer
 	Sess   quic.EarlySession
 	Err    error
 }
@@ -38,7 +39,7 @@ func TestHandshakeSaverSuccess(t *testing.T) {
 	}
 	saver := &trace.Saver{}
 	dlr := quicdialer.HandshakeSaver{
-		Dialer: &netxlite.QUICDialerQUICGo{
+		QUICDialer: &netxlite.QUICDialerQUICGo{
 			QUICListener: &netxlite.QUICListenerStdlib{},
 		},
 		Saver: saver,
@@ -96,7 +97,7 @@ func TestHandshakeSaverHostNameError(t *testing.T) {
 	}
 	saver := &trace.Saver{}
 	dlr := quicdialer.HandshakeSaver{
-		Dialer: &netxlite.QUICDialerQUICGo{
+		QUICDialer: &netxlite.QUICDialerQUICGo{
 			QUICListener: &netxlite.QUICListenerStdlib{},
 		},
 		Saver: saver,

internal/engine/netx/quicdialer/system.go

@@ -9,16 +9,10 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
 )
 
-// QUICListener listens for QUIC connections.
-type QUICListener interface {
-	// Listen creates a new listening UDPConn.
-	Listen(addr *net.UDPAddr) (model.UDPLikeConn, error)
-}
-
 // QUICListenerSaver is a QUICListener that also implements saving events.
 type QUICListenerSaver struct {
 	// QUICListener is the underlying QUICListener.
-	QUICListener QUICListener
+	model.QUICListener
 
 	// Saver is the underlying Saver.
 	Saver *trace.Saver