Subshells implemented using tornado event loops on 6.x branch #3305

Job	Run time
Test Lint	55s
check_release	1m 45s
test_docs	36s
test_without_debugpy (ubuntu-latest, 3.9)	2m 10s
build (ubuntu-latest, 3.9)	3m 18s
build (ubuntu-latest, 3.13)	3m 10s
Make SDist	21s
Test Minimum Versions	2m 22s
build (windows-latest, 3.9)	7m 52s
build (windows-latest, 3.13)	6m 34s
Test Prereleases	2m 9s
build (macos-latest, 3.9)	5m 58s
link_check	3m 24s
build (macos-latest, 3.13)	4m 20s
build (ubuntu-latest, pypy-3.9)	4m 16s
build (macos-latest, 3.10)	4m 32s
build (ubuntu-latest, 3.11)	3m 17s
build (ubuntu-latest, 3.12)	3m 33s
Install from SDist and Test	2m 12s
coverage	0s
	1h 2m 44s

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