p256: add 32-bit arithmetic and optimizations (#1033) #1951

Job	Run time
build (1.73.0, thumbv7em-none-eabi)	42s
build (1.73.0, wasm32-unknown-unknown)	41s
build (stable, thumbv7em-none-eabi)	29s
doc	1m 3s
build (stable, wasm32-unknown-unknown)	42s
test (i686-unknown-linux-gnu, 1.73.0, sudo apt update && sudo apt install gcc-multilib)	1m 57s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	2m 12s
test (x86_64-unknown-linux-gnu, 1.73.0)	1m 27s
test (x86_64-unknown-linux-gnu, stable)	1m 18s
cross (armv7-unknown-linux-gnueabihf, 1.73.0)	1m 45s
cross (armv7-unknown-linux-gnueabihf, stable)	1m 50s
cross (aarch64-unknown-linux-gnu, 1.73.0)	1m 43s
cross (aarch64-unknown-linux-gnu, stable)	2m 6s
cross (powerpc-unknown-linux-gnu, 1.73.0)	1m 55s
cross (powerpc-unknown-linux-gnu, stable)	2m 1s
	21m 51s

Provide feedback