Use `as_ref` instead of `as_slice` (#1336) #1061

Job	Run time
build-ksud (x86_64-linux-android) / build	2m 7s
build-ksud (x86_64-linux-android) / build	3m 30s
build-ksud (aarch64-linux-android) / build	2m 9s
build-ksud (aarch64-linux-android) / build	3m 33s
build-manager	3m 15s
build-manager	0s
	14m 34s

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