md5

blake2: restore `Blake2bVar`/`Blake2sVar` #1213

Job	Run time
set-msrv / set-msrv	5s
minimal-versions / minimal-versions	40s
build (1.85.0, loongarch64-unknown-linux-gnu)	25s
test (1.85.0)	36s
build (stable, thumbv7em-none-eabi)	29s
build (1.85.0, thumbv7em-none-eabi)	24s
test (stable)	34s
build (stable, wasm32-unknown-unknown)	31s
build (stable, loongarch64-unknown-linux-gnu)	27s
build (1.85.0, wasm32-unknown-unknown)	26s
	4m 37s

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