Feature: Sim mode at runtime #7034

Job	Run time
1/4	16m 8s
2/4	11m 32s
3/4	11m 23s
4/4	10m 53s
py-3-latest	18m 40s
flaky	6m 40s
_remote_background_indep_poll	4m 41s
_remote_background_indep_tcp	6m 47s
macos 1/5	20m 38s
macos 2/5	26m 10s
codecov	25s
	2h 13m 57s

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