Feature: Sim mode at runtime #7036

Job	Run time
1/4	13m 42s
2/4	12m 22s
3/4	11m 13s
4/4	11m 51s
py-3-latest	19m 5s
flaky	6m 41s
_remote_background_indep_poll	5m 3s
_remote_background_indep_tcp	6m 49s
macos 1/5	22m 1s
macos 2/5	24m 27s
codecov	19s
	2h 13m 33s

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