refactor(netxlite): use *Netx for creating TLS handshakers (#1252)

This diff is like
50279a7
but uses *Netx to create TLS handshakers.

The general idea of this patchset is to ensure we're not using duplicate
code for constructing netxlite types, which is good to do now, because
we're about to introduce new netxlite types for the network with which
we communicate with the OONI backend.

Reference issue: ooni/probe#2531

internal/netxlite/netx.go

@@ -22,12 +22,6 @@ func (netx *Netx) maybeCustomUnderlyingNetwork() *MaybeCustomUnderlyingNetwork {
 	return &MaybeCustomUnderlyingNetwork{netx.Underlying}
 }
 
-// NewTLSHandshakerStdlib is like [netxlite.NewTLSHandshakerStdlib] but the constructed [model.TLSHandshaker]
-// uses the [model.UnderlyingNetwork] configured inside the [Netx] structure.
-func (n *Netx) NewTLSHandshakerStdlib(logger model.DebugLogger) model.TLSHandshaker {
-	return newTLSHandshakerLogger(&tlsHandshakerConfigurable{provider: n.maybeCustomUnderlyingNetwork()}, logger)
-}
-
 // NewHTTPTransportStdlib is like [netxlite.NewHTTPTransportStdlib] but the constructed [model.HTTPTransport]
 // uses the [model.UnderlyingNetwork] configured inside the [Netx] structure.
 func (n *Netx) NewHTTPTransportStdlib(logger model.DebugLogger) model.HTTPTransport {

internal/netxlite/tls.go

@@ -163,8 +163,18 @@ var _ TLSConn = &tls.Conn{}
 //
 // 3. that we are going to use Mozilla CA if the [tls.Config]
 // RootCAs field is zero initialized.
+func (netx *Netx) NewTLSHandshakerStdlib(logger model.DebugLogger) model.TLSHandshaker {
+	return newTLSHandshakerLogger(
+		&tlsHandshakerConfigurable{provider: netx.maybeCustomUnderlyingNetwork()},
+		logger,
+	)
+}
+
+// NewTLSHandshakerStdlib is equivalent to creating an empty [*Netx]
+// and calling its NewTLSHandshakerStdlib method.
 func NewTLSHandshakerStdlib(logger model.DebugLogger) model.TLSHandshaker {
-	return newTLSHandshakerLogger(&tlsHandshakerConfigurable{}, logger)
+	netx := &Netx{Underlying: nil}
+	return netx.NewTLSHandshakerStdlib(logger)
 }
 
 // newTLSHandshakerLogger creates a new tlsHandshakerLogger instance.