Feature: Sim mode at runtime #6952

Job	Run time
1/4	16m 40s
2/4	11m 41s
3/4	11m 39s
4/4	11m 36s
py-3-latest	18m 15s
flaky	5m 47s
_remote_background_indep_poll	4m 55s
_remote_background_indep_tcp	6m 53s
macos 1/5	18m 49s
macos 2/5	23m 47s
codecov	0s
	2h 10m 2s

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