feat: add read/written bytes from/to request/response

Based on `count-response-size-middleware`.

lib/middlewares/addRWBytes.js

@@ -0,0 +1,15 @@
+const addRWBytes = () => (req, res, next) => {
+  const handle = () => {
+    res.removeListener('finish', handle)
+    res.removeListener('close', handle)
+    res.bytesRead = req.connection.bytesRead
+    res.bytesWritten = req.connection.bytesWritten
+  }
+
+  res.on('finish', handle)
+  res.on('close', handle)
+
+  next()
+}
+
+module.exports = addRWBytes