Support custom IOLOOPs

[gnir-work]

Summary

This is merge of two PR's

1. Allow passing a custom loop setup function instead of None #2391
   Support passing a custom IOLoop setup function in order to support running uvicorn in custom ioloop implementation other that the default and uvloop.
   For example this feature will allow using this monitored IOLoop inside uvicorn applications :)
   Link to discussions thread - Add support for custom ioloop implementations #2256

2. use asyncio.run(..., loop_factory) to avoid asyncio.set_event_loop_policy #2130
   set_event_loop_policy will be deprecated in python 3.13 and uvloop.EventLoopPolicy is deprecated already, this backports and uses the preferred loop_factory keyword to configure asyncio.run

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[gnir-work]

Not sure why @graingert removed this from here, please make sure its ok :)

[gnir-work]

Any updates regarding this? @Kludex

[gnir-work]

Hey guys,
Would really love to push this one forward.
We are currently having a real hard time integrating IOLoop monitoring because of the hacks needed when running a custom IOLoop implementation

Thanks :)