refactor(netx): move dialer's mockable types in mockablex (#368)

Part of https://github.com/ooni/probe/issues/1591

internal/engine/netx/dialer/logging_test.go

@@ -4,15 +4,21 @@ import (
 	"context"
 	"errors"
 	"io"
+	"net"
 	"testing"
 
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/dialer"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/mockablex"
 )
 
 func TestLoggingDialerFailure(t *testing.T) {
 	d := dialer.LoggingDialer{
-		Dialer: dialer.EOFDialer{},
+		Dialer: mockablex.Dialer{
+			MockDialContext: func(ctx context.Context, network string, address string) (net.Conn, error) {
+				return nil, io.EOF
+			},
+		},
 		Logger: log.Log,
 	}
 	conn, err := d.DialContext(context.Background(), "tcp", "www.google.com:443")