Add asyncio monitoring hooks

[achimnol (Joongi Kim)]

Yet another raise-up:

Measuring coroutine blocking time

I couldn’t find an easy way to measure how long an async coroutine blocks the event loop, so I rolled my own. I use this in conjunction with a lag monitor to keep track of event loop health and identify the next best targets for optimization. It’s difficult to maintain: every so often I come across a library that does something new that I haven’t accounted for. It breaks across different python versions sometimes too. I noticed that there are some coroutine time measurements in CPython. Is…