wip Flyte loop in FlyteContext & multi-threaded loops

[wild-endeavor]

This is a PR into #2752

Changes in this PR (move notes if merging)

• Create a new loop at module load time that is stored in the FlyteContext but is

  • not started
  • asyncio.set_event_loop is intentionally not called.
    The idea here is that the loop is protected because it's stored in a contextvar and is not associated directly with the asyncio library. However I've seen already one error associated with not calling set_event_loop and others may crop up. Not sure what Jupyter is doing, but if you try to create a new loop in Jupyter, and call asyncio.set_event_loop, it doesn't actually overwrite the event loop. If you call get_running_loop before and after set, it remains the same. Been looking through their code but not sure how they achieved this, they don't seem to be doing anything special.

• Introduce a threaded coroutine runner, along with helper functions. Basically if already in an async context, and another async function needs to be called from within a synchronous function, then a new thread will be used to run that coroutine and corresponding loop.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 19 lines in your changes missing coverage. Please review.

Please upload report for BASE (async/simple-te@c5a5a38). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
flytekit/utils/async_utils.py	84.48%	7 Missing and 2 partials ⚠️
flytekit/core/type_engine.py	77.14%	6 Missing and 2 partials ⚠️
flytekit/core/context_manager.py	86.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##             async/simple-te    #2759   +/-   ##
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  Coverage                   ?   72.34%           
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  Files                      ?      195           
  Lines                      ?    19946           
  Branches                   ?     3929           
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  Hits                       ?    14430           
  Misses                     ?     4813           
  Partials                   ?      703           

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