Subshells implemented using tornado event loops on 6.x branch #3362

Job	Run time
build (ubuntu-latest, 3.9)	4m 59s
check_release	1m 52s
link_check	3m 43s
build (ubuntu-latest, 3.13)	5m 6s
build (windows-latest, 3.9)	5m 57s
Make SDist	19s
build (windows-latest, 3.13)	5m 57s
test_docs	42s
build (macos-latest, 3.9)	5m 35s
build (macos-latest, 3.13)	5m 5s
Test Lint	45s
Test Minimum Versions	2m 32s
build (ubuntu-latest, pypy-3.9)	4m 27s
build (macos-latest, 3.10)	5m 11s
Test Prereleases	2m 10s
build (ubuntu-latest, 3.11)	4m 52s
test_without_debugpy (ubuntu-latest, 3.9)	2m 10s
build (ubuntu-latest, 3.12)	6m 0s
Install from SDist and Test	2m 15s
coverage	1s
	1h 9m 38s

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