k256+primeorder: add `BatchInvert` and `BatchNormalize` impls #139

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	5m 24s
build (1.65.0, wasm32-unknown-unknown)	3m 42s
cross (armv7-unknown-linux-gnueabihf, 1.65.0)	8m 42s
build (stable, thumbv7em-none-eabi)	12s
cross (armv7-unknown-linux-gnueabihf, stable)	1m 10s
build (stable, wasm32-unknown-unknown)	11s
cross (aarch64-unknown-linux-gnu, 1.65.0)	6m 59s
doc	14s
cross (aarch64-unknown-linux-gnu, stable)	1m 9s
cross (powerpc-unknown-linux-gnu, 1.65.0)	4m 37s
test (i686-unknown-linux-gnu, 1.65.0, sudo apt update && sudo apt install gcc-multilib)	8m 38s
cross (powerpc-unknown-linux-gnu, stable)	1m 15s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	2m 18s
test (x86_64-unknown-linux-gnu, 1.65.0)	4m 26s
test (x86_64-unknown-linux-gnu, stable)	54s
	49m 51s

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