k256

p521: simplify `FieldElement::from_uint_unchecked` #2118

Job	Run time
benches (1.73.0)	1m 22s
build (1.73.0, thumbv7em-none-eabi)	48s
benches (stable)	1m 15s
build (1.73.0, wasm32-unknown-unknown)	46s
cross (armv7-unknown-linux-gnueabihf, 1.73.0)	1m 25s
build (stable, thumbv7em-none-eabi)	39s
cross (armv7-unknown-linux-gnueabihf, stable)	1m 17s
doc	59s
build (stable, wasm32-unknown-unknown)	39s
cross (aarch64-unknown-linux-gnu, 1.73.0)	1m 33s
test (i686-unknown-linux-gnu, 1.73.0, sudo apt update && sudo apt install gcc-multilib)	1m 51s
cross (aarch64-unknown-linux-gnu, stable)	1m 29s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	1m 35s
cross (powerpc-unknown-linux-gnu, 1.73.0)	1m 35s
test (x86_64-unknown-linux-gnu, 1.73.0)	1m 30s
cross (powerpc-unknown-linux-gnu, stable)	1m 23s
test (x86_64-unknown-linux-gnu, stable)	1m 32s
	21m 38s

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