sha2

sha2: replace `soft` crate feature with configuration flag #1193

Job	Run time
riscv64-zknh	1m 47s
riscv32-zknh	1m 28s
minimal-versions / minimal-versions	42s
set-msrv / set-msrv	2s
macos (1.79.0)	20s
build (1.79.0, thumbv7em-none-eabi)	26s
macos (stable)	16s
linux (i686-unknown-linux-gnu, 1.79.0, sudo apt update && sudo apt install gcc-multilib)	1m 10s
build (1.79.0, wasm32-unknown-unknown)	29s
cross (1.79.0, aarch64-unknown-linux-gnu, default)	40s
linux (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	54s
build (1.79.0, loongarch64-unknown-linux-gnu)	26s
cross (1.79.0, powerpc-unknown-linux-gnu, default)	38s
linux (x86_64-unknown-linux-gnu, 1.79.0)	46s
windows (1.79.0, x86_64-pc-windows-gnu)	58s
build (stable, thumbv7em-none-eabi)	20s
linux (x86_64-unknown-linux-gnu, stable)	36s
cross (stable, aarch64-unknown-linux-gnu, default)	36s
windows (stable, x86_64-pc-windows-gnu)	1m 58s
build (stable, wasm32-unknown-unknown)	25s
cross (stable, powerpc-unknown-linux-gnu, default)	38s
build (stable, loongarch64-unknown-linux-gnu)	21s
	15m 56s

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