Add async to instantiate #664

Job	Run time
rust_ci (windows-latest, stable)	2m 6s
rust_ci (ubuntu-latest, beta)	52s
rust_ci (macos-latest, stable)	1m 17s
rust_ci (ubuntu-latest, stable)	1m 6s
rust_ci (macos-latest, beta)	1m 6s
rust_ci (windows-latest, beta)	1m 47s
	8m 14s

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