Subshells implemented using tornado event loops on 6.x branch #3319

Job	Run time
build (ubuntu-latest, 3.9)	7m 35s
build (ubuntu-latest, 3.13)	2m 27s
check_release	1m 37s
build (windows-latest, 3.9)	8m 44s
test_docs	37s
build (windows-latest, 3.13)	6m 26s
build (macos-latest, 3.9)	4m 49s
Test Lint	53s
test_without_debugpy (ubuntu-latest, 3.9)	7m 4s
build (macos-latest, 3.13)	4m 31s
build (ubuntu-latest, pypy-3.9)	4m 41s
link_check	3m 29s
build (macos-latest, 3.10)	4m 50s
build (ubuntu-latest, 3.11)	2m 25s
Make SDist	20s
Test Minimum Versions	2m 24s
build (ubuntu-latest, 3.12)	2m 52s
Test Prereleases	7m 8s
Install from SDist and Test	2m 17s
coverage	0s
	1h 15m 9s

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