refactor: move httptransport w/ logging to netxlite (#411)

Part of https://github.com/ooni/probe/issues/1505

internal/netxmocks/http.go

@@ -0,0 +1,19 @@
+package netxmocks
+
+import "net/http"
+
+// HTTPTransport mocks netxlite.HTTPTransport.
+type HTTPTransport struct {
+	MockRoundTrip            func(req *http.Request) (*http.Response, error)
+	MockCloseIdleConnections func()
+}
+
+// RoundTrip calls MockRoundTrip.
+func (txp *HTTPTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	return txp.MockRoundTrip(req)
+}
+
+// CloseIdleConnections calls MockCloseIdleConnections.
+func (txp *HTTPTransport) CloseIdleConnections() {
+	txp.MockCloseIdleConnections()
+}