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[WIP] MD6 implementation #974

Job	Run time
loongarch64_asm	16s
test-msrv	11s
minimal-versions / minimal-versions	4m 49s
set-msrv / set-msrv	4s
build (1.59, thumbv7em-none-eabi)	4m 4s
build (1.59, wasm32-unknown-unknown)	3m 59s
macos (1.59.0)	6m 55s
build (stable, thumbv7em-none-eabi)	27s
linux (i686-unknown-linux-gnu, 1.59.0, sudo apt update && sudo apt install gcc-multilib)	4m 10s
macos (stable)	55s
cross (1.59.0, aarch64-unknown-linux-gnu, default)	3m 54s
build (stable, wasm32-unknown-unknown)	31s
linux (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	4m 5s
cross (1.59.0, powerpc-unknown-linux-gnu, default)	3m 50s
linux (x86_64-unknown-linux-gnu, 1.59.0)	3m 48s
cross (stable, aarch64-unknown-linux-gnu, default)	52s
linux (x86_64-unknown-linux-gnu, stable)	3m 4s
windows (1.59.0, x86_64-pc-windows-gnu)	5m 12s
cross (stable, powerpc-unknown-linux-gnu, default)	52s
windows (stable, x86_64-pc-windows-gnu)	1m 4s
cross (stable, aarch64-unknown-linux-gnu, asm)	52s
	53m 54s

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