feat: Configuration option for setting default loop_scope for tests

[Novakov]

New configuration option, asyncio_default_test_loop_scope, provides default value for loop_scope argument of asyncio marker. This can be used to use the same event loop in auto mode without need to use modifyitems hook.

Test functions can still override loop_scope by using asyncio marker.

Implements #793

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.24%. Comparing base (623ab74) to head (5272cc4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1035      +/-   ##
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+ Coverage   91.10%   91.24%   +0.14%     
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  Files           2        2              
  Lines         562      571       +9     
  Branches       74       75       +1     
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+ Hits          512      521       +9     
  Misses         30       30              
  Partials       20       20              

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[seifertm]

Thank you! I really like how you changed _get_marked_loop_scope and how you used functions to keep the code readable.

Can you please add an entry to docs/reference/changelog.rst where you link to #793 ?
Assume that this PR bumps the minor version and set the date to UNRELEASED.

[seifertm]

It's nothing short of great that you even included a how-to guide for the new approach, thanks!

[seifertm]

I think we can drop the "run_session_tests_in_same_loop" how-to guide. It's superseded by the configuration option. I cannot think of a use case where someone wants to use the pytest hook, instead of the config option.