Adopt ExceptionGroup handling without an external library

[penguinolog]

• Python <3.11 behaviour not changed

Fix: #893

Checklist

• I've ensured that similar functionality has not already been implemented
• I've ensured that similar functionality has not earlier been proposed and declined
• I've branched off the master or python-dual-support branch
• I've merged fresh upstream into my branch recently
• I've ran tox successfully in local environment
• I've included docstrings and/or documentation and/or examples for my code (if this is a new feature)

[coveralls]

Pull Request Test Coverage Report for Build 9396365651

Details

• 7 of 10 (70.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.001%) to 74.719%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
urwid/event_loop/trio_loop.py	7	10	70.0%

Totals
Change from base Build 9347791057:	0.001%
Covered Lines:	9405
Relevant Lines:	12734

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💛 - Coveralls