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/engine/legacy/netx/emitterdialer_test.go

@@ -10,7 +10,7 @@ import (
 
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/handlers"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/modelx"
-	"github.com/ooni/probe-cli/v3/internal/netxmocks"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/mocks"
 )
 
 func TestEmitterFailure(t *testing.T) {
@@ -20,7 +20,7 @@ func TestEmitterFailure(t *testing.T) {
 		Beginning: time.Now(),
 		Handler:   saver,
 	})
-	d := EmitterDialer{Dialer: &netxmocks.Dialer{
+	d := EmitterDialer{Dialer: &mocks.Dialer{
 		MockDialContext: func(ctx context.Context, network string, address string) (net.Conn, error) {
 			return nil, io.EOF
 		},
@@ -69,9 +69,9 @@ func TestEmitterSuccess(t *testing.T) {
 		Beginning: time.Now(),
 		Handler:   saver,
 	})
-	d := EmitterDialer{Dialer: &netxmocks.Dialer{
+	d := EmitterDialer{Dialer: &mocks.Dialer{
 		MockDialContext: func(ctx context.Context, network string, address string) (net.Conn, error) {
-			return &netxmocks.Conn{
+			return &mocks.Conn{
 				MockRead: func(b []byte) (int, error) {
 					return 0, io.EOF
 				},

internal/engine/legacy/netx/http_test.go

@@ -14,7 +14,7 @@ import (
 
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx"
 	"github.com/ooni/probe-cli/v3/internal/errorsx"
-	"github.com/ooni/probe-cli/v3/internal/iox"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/iox"
 )
 
 func dowithclient(t *testing.T, client *netx.HTTPClient) {

internal/engine/legacy/netx/oldhttptransport/bodytracer_test.go

@@ -5,7 +5,7 @@ import (
 	"net/http"
 	"testing"
 
-	"github.com/ooni/probe-cli/v3/internal/iox"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/iox"
 )
 
 func TestBodyTracerSuccess(t *testing.T) {

internal/engine/legacy/netx/oldhttptransport/httptransport_test.go

@@ -5,7 +5,7 @@ import (
 	"net/http"
 	"testing"
 
-	"github.com/ooni/probe-cli/v3/internal/iox"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/iox"
 )
 
 func TestGood(t *testing.T) {

internal/engine/legacy/netx/oldhttptransport/tracetripper.go

@@ -13,7 +13,7 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/atomicx"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/modelx"
 	"github.com/ooni/probe-cli/v3/internal/errorsx"
-	"github.com/ooni/probe-cli/v3/internal/iox"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/iox"
 )
 
 // TraceTripper performs single HTTP transactions.

internal/engine/legacy/netx/oldhttptransport/tracetripper_test.go

@@ -13,7 +13,7 @@ import (
 
 	"github.com/miekg/dns"
 	"github.com/ooni/probe-cli/v3/internal/engine/legacy/netx/modelx"
-	"github.com/ooni/probe-cli/v3/internal/iox"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/iox"
 )
 
 func TestTraceTripperSuccess(t *testing.T) {