k256

use new arith api #15

Job	Run time
benches (1.81.0)	1m 28s
benches (stable)	1m 6s
build (1.81.0, thumbv7em-none-eabi)	46s
cross (armv7-unknown-linux-gnueabihf, 1.81.0)	1m 25s
build (1.81.0, wasm32-unknown-unknown)	43s
doc	1m 8s
cross (armv7-unknown-linux-gnueabihf, stable)	1m 13s
build (stable, thumbv7em-none-eabi)	42s
test (i686-unknown-linux-gnu, 1.81.0, sudo apt update && sudo apt install gcc-multilib)	1m 44s
cross (aarch64-unknown-linux-gnu, 1.81.0)	1m 19s
build (stable, wasm32-unknown-unknown)	38s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	1m 45s
cross (aarch64-unknown-linux-gnu, stable)	1m 15s
test (x86_64-unknown-linux-gnu, 1.81.0)	1m 24s
cross (powerpc-unknown-linux-gnu, 1.81.0)	1m 28s
test (x86_64-unknown-linux-gnu, stable)	1m 29s
cross (powerpc-unknown-linux-gnu, stable)	1m 16s
	20m 49s

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