k256

p521: Update `fiat-crypto` + `fiat-constify` #1962

Job	Run time
benches (1.65.0)	6m 49s
build (1.65.0, thumbv7em-none-eabi)	6m 56s
benches (stable)	2m 49s
build (1.65.0, wasm32-unknown-unknown)	6m 17s
build (stable, thumbv7em-none-eabi)	1m 14s
cross (armv7-unknown-linux-gnueabihf, 1.65.0)	7m 45s
build (stable, wasm32-unknown-unknown)	56s
cross (armv7-unknown-linux-gnueabihf, stable)	2m 7s
cross (aarch64-unknown-linux-gnu, 1.65.0)	8m 6s
cross (aarch64-unknown-linux-gnu, stable)	2m 43s
doc	25s
cross (powerpc-unknown-linux-gnu, 1.65.0)	7m 42s
cross (powerpc-unknown-linux-gnu, stable)	2m 17s
test (i686-unknown-linux-gnu, 1.65.0, sudo apt update && sudo apt install gcc-multilib)	9m 22s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	3m 36s
test (x86_64-unknown-linux-gnu, 1.65.0)	7m 12s
test (x86_64-unknown-linux-gnu, stable)	2m 12s
	1h 18m 28s

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