p521

k256+primeorder: add `batch_normalize_generic` #817

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	6m 28s
build (1.65.0, wasm32-unknown-unknown)	3m 45s
build (stable, thumbv7em-none-eabi)	15s
doc	23s
build (stable, wasm32-unknown-unknown)	23s
test (i686-unknown-linux-gnu, 1.65.0, sudo apt update && sudo apt install gcc-multilib)	8m 11s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	2m 2s
test (x86_64-unknown-linux-gnu, 1.65.0)	4m 25s
test (x86_64-unknown-linux-gnu, stable)	1m 0s
	26m 52s

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