refactor: interfaces and data types into the model package (#642)

## Checklist

- [x] I have read the [contribution guidelines](https://github.com/ooni/probe-cli/blob/master/CONTRIBUTING.md)
- [x] reference issue for this pull request: https://github.com/ooni/probe/issues/1885
- [x] related ooni/spec pull request: N/A

Location of the issue tracker: https://github.com/ooni/probe

## Description

This PR contains a set of changes to move important interfaces and data types into the `./internal/model` package.

The criteria for including an interface or data type in here is roughly that the type should be important and used by several packages. We are especially interested to move more interfaces here to increase modularity.

An additional side effect is that, by reading this package, one should be able to understand more quickly how different parts of the codebase interact with each other.

This is what I want to move in `internal/model`:

- [x] most important interfaces from `internal/netxlite`
- [x] everything that was previously part of `internal/engine/model`
- [x] mocks from `internal/netxlite/mocks` should also be moved in here as a subpackage

internal/netxlite/http.go

@@ -8,20 +8,12 @@ import (
 	"time"
 
 	oohttp "github.com/ooni/oohttp"
+	"github.com/ooni/probe-cli/v3/internal/model"
 )
 
-// HTTPTransport is an http.Transport-like structure.
-type HTTPTransport interface {
-	// RoundTrip performs the HTTP round trip.
-	RoundTrip(req *http.Request) (*http.Response, error)
-
-	// CloseIdleConnections closes idle connections.
-	CloseIdleConnections()
-}
-
 // httpTransportErrWrapper is an HTTPTransport with error wrapping.
 type httpTransportErrWrapper struct {
-	HTTPTransport
+	model.HTTPTransport
 }
 
 func (txp *httpTransportErrWrapper) RoundTrip(req *http.Request) (*http.Response, error) {
@@ -35,13 +27,13 @@ func (txp *httpTransportErrWrapper) RoundTrip(req *http.Request) (*http.Response
 // httpTransportLogger is an HTTPTransport with logging.
 type httpTransportLogger struct {
 	// HTTPTransport is the underlying HTTP transport.
-	HTTPTransport HTTPTransport
+	HTTPTransport model.HTTPTransport
 
 	// Logger is the underlying logger.
-	Logger Logger
+	Logger model.DebugLogger
 }
 
-var _ HTTPTransport = &httpTransportLogger{}
+var _ model.HTTPTransport = &httpTransportLogger{}
 
 func (txp *httpTransportLogger) RoundTrip(req *http.Request) (*http.Response, error) {
 	txp.Logger.Debugf("> %s %s", req.Method, req.URL.String())
@@ -73,9 +65,9 @@ func (txp *httpTransportLogger) CloseIdleConnections() {
 // httpTransportConnectionsCloser is an HTTPTransport that
 // correctly forwards CloseIdleConnections calls.
 type httpTransportConnectionsCloser struct {
-	HTTPTransport
-	Dialer
-	TLSDialer
+	model.HTTPTransport
+	model.Dialer
+	model.TLSDialer
 }
 
 // CloseIdleConnections forwards the CloseIdleConnections calls.
@@ -89,7 +81,7 @@ func (txp *httpTransportConnectionsCloser) CloseIdleConnections() {
 //
 // This factory and NewHTTPTransportStdlib are the recommended
 // ways of creating a new HTTPTransport.
-func NewHTTPTransport(logger Logger, dialer Dialer, tlsDialer TLSDialer) HTTPTransport {
+func NewHTTPTransport(logger model.DebugLogger, dialer model.Dialer, tlsDialer model.TLSDialer) model.HTTPTransport {
 	return WrapHTTPTransport(logger, NewOOHTTPBaseTransport(dialer, tlsDialer))
 }
 
@@ -117,7 +109,7 @@ func NewHTTPTransport(logger Logger, dialer Dialer, tlsDialer TLSDialer) HTTPTra
 // way in which we perform measurements.
 //
 // This is a low level factory. Consider not using it directly.
-func NewOOHTTPBaseTransport(dialer Dialer, tlsDialer TLSDialer) HTTPTransport {
+func NewOOHTTPBaseTransport(dialer model.Dialer, tlsDialer model.TLSDialer) model.HTTPTransport {
 	// Using oohttp to support any TLS library.
 	txp := oohttp.DefaultTransport.(*oohttp.Transport).Clone()
 
@@ -158,7 +150,7 @@ func NewOOHTTPBaseTransport(dialer Dialer, tlsDialer TLSDialer) HTTPTransport {
 // and guarantees that returned errors are wrapped.
 //
 // This is a low level factory. Consider not using it directly.
-func WrapHTTPTransport(logger Logger, txp HTTPTransport) HTTPTransport {
+func WrapHTTPTransport(logger model.DebugLogger, txp model.HTTPTransport) model.HTTPTransport {
 	return &httpTransportLogger{
 		HTTPTransport: &httpTransportErrWrapper{txp},
 		Logger:        logger,
@@ -168,7 +160,7 @@ func WrapHTTPTransport(logger Logger, txp HTTPTransport) HTTPTransport {
 // httpDialerWithReadTimeout enforces a read timeout for all HTTP
 // connections. See https://github.com/ooni/probe/issues/1609.
 type httpDialerWithReadTimeout struct {
-	Dialer
+	model.Dialer
 }
 
 // DialContext implements Dialer.DialContext.
@@ -184,7 +176,7 @@ func (d *httpDialerWithReadTimeout) DialContext(
 // httpTLSDialerWithReadTimeout enforces a read timeout for all HTTP
 // connections. See https://github.com/ooni/probe/issues/1609.
 type httpTLSDialerWithReadTimeout struct {
-	TLSDialer
+	model.TLSDialer
 }
 
 // ErrNotTLSConn occur when an interface accepts a net.Conn but
@@ -259,25 +251,19 @@ func (c *httpTLSConnWithReadTimeout) Read(b []byte) (int, error) {
 //
 // This factory and NewHTTPTransport are the recommended
 // ways of creating a new HTTPTransport.
-func NewHTTPTransportStdlib(logger Logger) HTTPTransport {
+func NewHTTPTransportStdlib(logger model.DebugLogger) model.HTTPTransport {
 	dialer := NewDialerWithResolver(logger, NewResolverStdlib(logger))
 	tlsDialer := NewTLSDialer(dialer, NewTLSHandshakerStdlib(logger))
 	return NewHTTPTransport(logger, dialer, tlsDialer)
 }
 
-// HTTPClient is an http.Client-like interface.
-type HTTPClient interface {
-	Do(req *http.Request) (*http.Response, error)
-	CloseIdleConnections()
-}
-
 // WrapHTTPClient wraps an HTTP client to add error wrapping capabilities.
-func WrapHTTPClient(clnt HTTPClient) HTTPClient {
+func WrapHTTPClient(clnt model.HTTPClient) model.HTTPClient {
 	return &httpClientErrWrapper{clnt}
 }
 
 type httpClientErrWrapper struct {
-	HTTPClient
+	model.HTTPClient
 }
 
 func (c *httpClientErrWrapper) Do(req *http.Request) (*http.Response, error) {