lib: add trace support for client reads and writes

- add `CURL_TRC_READ()` and `CURL_TRC_WRITE()`
- use in generic client writers and readers, as well
  as http headers, chunking and websockets

Closes #13223

lib/transfer.c

@@ -1190,6 +1190,8 @@ CURLcode Curl_xfer_write_resp(struct Curl_easy *data,
     data->req.eos_written = TRUE;
     data->req.download_done = TRUE;
   }
+  CURL_TRC_WRITE(data, "xfer_write_resp(len=%zu, eos=%d) -> %d",
+                 blen, is_eos, result);
   return result;
 }