Add experimental runner to run fixture setup and teardown in a single task

[tjkuson]

No description provided.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 75.89928% with 67 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.20%. Comparing base (cb94811) to head (312406e).
⚠️ Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
pytest_asyncio/_runner.py	64.53%	54 Missing and 7 partials ⚠️
pytest_asyncio/plugin.py	94.33%	6 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (cb94811) and HEAD (312406e). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (cb94811)	HEAD (312406e)
	2	1

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1579      +/-   ##
==========================================
- Coverage   94.50%   88.20%   -6.31%     
==========================================
  Files           2        3       +1     
  Lines         510      780     +270     
  Branches       62       88      +26     
==========================================
+ Hits          482      688     +206     
- Misses         22       79      +57     
- Partials        6       13       +7     

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