code: def fetch_impl(
      self,
      request: HTTPRequest,
      callback: Callable[[HTTPResponse], None],
  ) -> None:
      self._requests.append((request, callback, self.io_loop.time()))
      self._process_queue()
      self._set_timeout(0)
  
imports: import collections
  import functools
  import logging
  import pycurl
  import threading
  import time
  from io import BytesIO
  from tornado import httputil
  from tornado import ioloop
  from tornado.escape import utf8, native_str
  from tornado.httpclient import HTTPRequest, HTTPResponse, HTTPError, AsyncHTTPClient, main
  from tornado.log import app_log
  from typing import Dict, Any, Callable, Union, Optional
  import typing
label_desc: Use image node_id 3 for calling the CurlAsyncHTTPClient obj's underlying member method code with example usage: obj.fetch_impl(request, callback) without return types