refactor: move base http3 transport into netxlite (#412)

This diff is part of https://github.com/ooni/probe/issues/1505.

You will notice that I have not adapted all the (great) tests we had
previously. They should live at another layer, and namely the one that
deals with performing measurements.

When I'm refactoring such a layer I'll ensure those tests that I have
not adapted here are reintroduced into the tree.

internal/engine/netx/httptransport/http3transport.go

@@ -1,43 +1,10 @@
 package httptransport
 
 import (
-	"context"
-	"crypto/tls"
-	"net/http"
-
-	"github.com/lucas-clemente/quic-go"
-	"github.com/lucas-clemente/quic-go/http3"
-	"github.com/ooni/probe-cli/v3/internal/engine/netx/quicdialer"
+	"github.com/ooni/probe-cli/v3/internal/netxlite"
 )
 
-// QUICWrapperDialer is a QUICDialer that wraps a ContextDialer
-// This is necessary because the http3 RoundTripper does not support a DialContext method.
-type QUICWrapperDialer struct {
-	Dialer quicdialer.ContextDialer
-}
-
-// Dial implements QUICDialer.Dial
-func (d QUICWrapperDialer) Dial(network, host string, tlsCfg *tls.Config, cfg *quic.Config) (quic.EarlySession, error) {
-	return d.Dialer.DialContext(context.Background(), network, host, tlsCfg, cfg)
-}
-
-// HTTP3Transport is a httptransport.RoundTripper using the http3 protocol.
-type HTTP3Transport struct {
-	http3.RoundTripper
-}
-
-// CloseIdleConnections closes all the connections opened by this transport.
-func (t *HTTP3Transport) CloseIdleConnections() {
-	t.RoundTripper.Close()
-}
-
 // NewHTTP3Transport creates a new HTTP3Transport instance.
 func NewHTTP3Transport(config Config) RoundTripper {
-	txp := &HTTP3Transport{}
-	txp.QuicConfig = &quic.Config{}
-	txp.TLSClientConfig = config.TLSConfig
-	txp.Dial = config.QUICDialer.Dial
-	return txp
+	return netxlite.NewHTTP3Transport(config.QUICDialer, config.TLSConfig)
 }
-
-var _ RoundTripper = &http.Transport{}