refactor(netxlite): hide details without breaking the rest of the tree (#454)

## Description

This PR continues the refactoring of `netx` under the following principles:

1. do not break the rest of the tree and do not engage in extensive tree-wide refactoring yet
2. move under `netxlite` clearly related subpackages (e.g., `iox`, `netxmocks`)
3. move into `internal/netxlite/internal` stuff that is clearly private of `netxlite`
4. hide implementation details in `netxlite` pending new factories
5. refactor `tls` code in `netxlite` to clearly separate `crypto/tls` code from `utls` code

After each commit, I run `go test -short -race ./...` locally. Each individual commit explains what it does. I will squash, but this operation will preserve the original commit titles, so this will give further insight on each step.

## Commits

* refactor: rename netxmocks -> netxlite/mocks

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

* refactor: rename quicx -> netxlite/quicx

See https://github.com/ooni/probe/issues/1591

* refactor: rename iox -> netxlite/iox

Regenerate sources and make sure the tests pass.

See https://github.com/ooni/probe/issues/1591.

* refactor(iox): move MockableReader to netxlite/mocks

See https://github.com/ooni/probe/issues/1591

* refactor(netxlite): generator is an implementation detail

See https://github.com/ooni/probe/issues/1591

* refactor(netxlite): separate tls and utls code

See https://github.com/ooni/probe/issues/1591

* refactor(netxlite): hide most types but keep old names as legacy

With this change we avoid breaking the rest of the tree, but we start
hiding some implementation details a bit. Factories will follow.

See https://github.com/ooni/probe/issues/1591

internal/ptx/obfs4_test.go

@@ -9,7 +9,7 @@ import (
 	"testing"
 
 	"github.com/ooni/probe-cli/v3/internal/atomicx"
-	"github.com/ooni/probe-cli/v3/internal/netxmocks"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/mocks"
 )
 
 func TestOBFS4DialerWorks(t *testing.T) {
@@ -49,7 +49,7 @@ func TestOBFS4DialerFailsWithInvalidCert(t *testing.T) {
 func TestOBFS4DialerFailsWithConnectionErrorAndNoContextExpiration(t *testing.T) {
 	expected := errors.New("mocked error")
 	o4d := DefaultTestingOBFS4Bridge()
-	o4d.UnderlyingDialer = &netxmocks.Dialer{
+	o4d.UnderlyingDialer = &mocks.Dialer{
 		MockDialContext: func(ctx context.Context, network string, address string) (net.Conn, error) {
 			return nil, expected
 		},
@@ -71,7 +71,7 @@ func TestOBFS4DialerFailsWithConnectionErrorAndContextExpiration(t *testing.T) {
 	sigch := make(chan interface{})
 	wg := &sync.WaitGroup{}
 	wg.Add(1)
-	o4d.UnderlyingDialer = &netxmocks.Dialer{
+	o4d.UnderlyingDialer = &mocks.Dialer{
 		MockDialContext: func(ctx context.Context, network string, address string) (net.Conn, error) {
 			cancel()
 			<-sigch
@@ -107,7 +107,7 @@ func TestOBFS4DialerWorksWithContextExpiration(t *testing.T) {
 	defer cancel()
 	called := &atomicx.Int64{}
 	o4d := DefaultTestingOBFS4Bridge()
-	o4d.UnderlyingDialer = &netxmocks.Dialer{
+	o4d.UnderlyingDialer = &mocks.Dialer{
 		MockDialContext: func(ctx context.Context, network string, address string) (net.Conn, error) {
 			// We cancel the context before returning the error, which makes
 			// the context cancellation happen before us returning.

internal/ptx/ptx.go

@@ -45,7 +45,7 @@ import (
 	"sync"
 
 	pt "git.torproject.org/pluggable-transports/goptlib.git"
-	"github.com/ooni/probe-cli/v3/internal/iox"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/iox"
 )
 
 // PTDialer is a generic pluggable transports dialer.

internal/ptx/ptx_test.go

@@ -13,8 +13,8 @@ import (
 
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/v3/internal/atomicx"
-	"github.com/ooni/probe-cli/v3/internal/iox"
-	"github.com/ooni/probe-cli/v3/internal/netxmocks"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/iox"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/mocks"
 )
 
 func TestListenerLoggerWorks(t *testing.T) {
@@ -96,8 +96,8 @@ func TestListenerCastListenerWorksFineOnError(t *testing.T) {
 
 // mockableSocksConn is a mockable ptxSocksConn.
 type mockableSocksConn struct {
-	// netxmocks.Conn allows to mock all net.Conn functionality.
-	*netxmocks.Conn
+	// mocks.Conn allows to mock all net.Conn functionality.
+	*mocks.Conn
 
 	// MockGrant allows to mock the Grant function.
 	MockGrant func(addr *net.TCPAddr) error
@@ -160,7 +160,7 @@ func TestListenerHandleSocksConnWithDialContextFailure(t *testing.T) {
 	}
 	lst := &Listener{PTDialer: d}
 	c := &mockableSocksConn{
-		Conn: &netxmocks.Conn{
+		Conn: &mocks.Conn{
 			MockClose: func() error {
 				return nil
 			},

internal/ptx/snowflake_test.go

@@ -7,7 +7,7 @@ import (
 	"testing"
 
 	"github.com/ooni/probe-cli/v3/internal/atomicx"
-	"github.com/ooni/probe-cli/v3/internal/netxmocks"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/mocks"
 )
 
 func TestSnowflakeDialerWorks(t *testing.T) {
@@ -50,7 +50,7 @@ func TestSnowflakeDialerWorksWithMocks(t *testing.T) {
 		newClientTransport: func(brokerURL, frontDomain string, iceAddresses []string, keepLocalAddresses bool, maxSnowflakes int) (snowflakeTransport, error) {
 			return &mockableSnowflakeTransport{
 				MockDial: func() (net.Conn, error) {
-					return &netxmocks.Conn{
+					return &mocks.Conn{
 						MockClose: func() error {
 							return nil
 						},
@@ -144,7 +144,7 @@ func TestSnowflakeDialerWorksWithWithCancelledContext(t *testing.T) {
 			return &mockableSnowflakeTransport{
 				MockDial: func() (net.Conn, error) {
 					cancel() // cause a cancel before we can really have a conn
-					return &netxmocks.Conn{
+					return &mocks.Conn{
 						MockClose: func() error {
 							called.Add(1)
 							return nil