Subshells implemented using tornado event loops on 6.x branch #3316

Job	Run time
build (ubuntu-latest, 3.9)	2m 25s
check_release	1m 48s
build (ubuntu-latest, 3.13)	2m 20s
Make SDist	26s
build (windows-latest, 3.9)	8m 55s
build (windows-latest, 3.13)	7m 35s
test_docs	34s
Test Lint	59s
build (macos-latest, 3.9)	5m 0s
build (macos-latest, 3.13)	4m 35s
build (ubuntu-latest, pypy-3.9)	4m 20s
Test Prereleases	2m 4s
Test Minimum Versions	2m 18s
build (macos-latest, 3.10)	7m 42s
build (ubuntu-latest, 3.11)	7m 22s
test_without_debugpy (ubuntu-latest, 3.9)	7m 1s
build (ubuntu-latest, 3.12)	5m 47s
link_check	3m 31s
Install from SDist and Test	2m 8s
coverage	0s
	1h 16m 50s

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