Subshells implemented using tornado event loops on 6.x branch #3366

Job	Run time
Test Lint	56s
Make SDist	24s
build (ubuntu-latest, 3.9)	4m 56s
build (ubuntu-latest, 3.13)	5m 7s
Test Minimum Versions	2m 36s
Test Prereleases	2m 20s
test_without_debugpy (ubuntu-latest, 3.9)	2m 6s
build (windows-latest, 3.9)	6m 23s
build (windows-latest, 3.13)	7m 57s
link_check	3m 29s
build (macos-latest, 3.9)	5m 21s
test_docs	39s
build (macos-latest, 3.13)	4m 57s
build (ubuntu-latest, pypy-3.9)	4m 33s
build (macos-latest, 3.10)	4m 55s
build (ubuntu-latest, 3.11)	4m 47s
build (ubuntu-latest, 3.12)	5m 54s
check_release	1m 50s
Install from SDist and Test	2m 24s
coverage	11s
	1h 11m 45s

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