dhkem

Add sntrup-kem #598

Job	Run time
set-msrv / set-msrv	9s
minimal-versions	0s
cross (powerpc-unknown-linux-gnu, 1.85.0)	55s
cross (powerpc-unknown-linux-gnu, stable)	49s
test (1.85.0)	34s
test (stable)	1m 0s
no_std (stable, thumbv7em-none-eabi)	22s
no_std (1.85.0, wasm32-unknown-unknown)	23s
no_std (1.85.0, thumbv7em-none-eabi)	24s
no_std (stable, wasm32-unknown-unknown)	20s
	4m 56s

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