Just delay select.epoll to fix import after gevent monkey patching

[A5rocks]

This seems to work:

Python 3.9.2 (default, Feb 28 2021, 17:03:44)
[GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import gevent.monkey
>>> gevent.monkey.patch_all()
True
>>> import trio
>>> exit()

Fixes: #2848

... While trio still doesn't work under gevent, I think not erroring when importing is a good property to have.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.63%. Comparing base (71457f7) to head (4bd7afa).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2928   +/-   ##
=======================================
  Coverage   99.63%   99.63%           
=======================================
  Files         120      120           
  Lines       17865    17865           
  Branches     3212     3213    +1     
=======================================
  Hits        17800    17800           
  Misses         46       46           
  Partials       19       19           

Files with missing lines	Coverage Δ
src/trio/_core/_io_epoll.py	100.00% <100.00%> (ø)

[A5rocks]

cc @jeongilpark could you see if this works for you? I'm not sure if you're actually ending up using trio. (if you do, maybe we should do a better solution, like... I don't know, maybe use gevent.monkey.get_original? or... idk this level of trio very well.)

[neevista]

@jakkdl @CoolCat467 - is this issue and the one specifically listed below resolved now?

gevent/gevent#2008

[jakkdl]

@jakkdl @CoolCat467 - is this issue and the one specifically listed below resolved now?

gevent/gevent#2008

no? I don't see any reason why they've would've been fixed with no changes to any code.

[CoolCat467]

Seems simple enough, while obviously not fixing the underlying issue I think not crashing on import is important.

[TeamSpen210]

Might be a good idea to add a comment as to why we're using a lambda here. Otherwise someone coming along in the future might "optimise" that out, especially since I know PyLint and therefore Ruff has a rule which would flag this.