[feature request] add loop._run_once and loop._set_is_runnning api to easy the process of OS gui event loop integrate

[congzhangzh]

• uvloop version:
  latest

• Python version:
  3.11.2

• Platform:
  All, and testing on Linux

• Can you reproduce the bug with PYTHONASYNCIODEBUG in env?:
  n.a

• Does uvloop behave differently from vanilla asyncio? How?:
  no

• Purpose:
  Add a public API to

1. setting running state
2. allow run_once of event loop

• Background:

I want to pull the event from backend_fd from another process and process them on os GUI event loop which like electron, but uvloop has no public API to run_once and keep _is_running

• Refs:

1. https://discuss.python.org/t/connecting-asyncio-and-tkinter-event-loops/14722/9
2. [feature request] add async function bind support congzhangzh/webview_python#1

[congzhangzh]

ref: https://github.com/congzhangzh/uvloop