Add async `ready` support #347

Job	Run time
check (1.70.0, windows-latest)	43m 17s
check (1.70.0, ubuntu-latest)	1m 13s
check (stable, windows-latest)	1m 41s
check (stable, ubuntu-latest)	21s
check (nightly, windows-latest)	45s
check (nightly, ubuntu-latest)	25s
	47m 42s

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