Add `AsyncEnumerable` #639

Job	Run time
Test (Release, Pool_Enabled)	1m 58s
Test (Release, Pool_Disabled)	1m 58s
Test (Release_NoProgress, Pool_Enabled)	1m 58s
Test (Release_NoProgress, Pool_Disabled)	1m 59s
Test (Debug, Pool_Disabled)	2m 2s
Test (Debug_NoProgress, Pool_Disabled)	2m 52s
	12m 47s

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