k256: check for R being the identity point on Schnorr verification (#… #56

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	1m 59s
build (1.65.0, wasm32-unknown-unknown)	1m 31s
build (stable, thumbv7em-none-eabi)	17s
build (stable, wasm32-unknown-unknown)	20s
cross (armv7-unknown-linux-gnueabihf, 1.65.0)	3m 30s
cross (armv7-unknown-linux-gnueabihf, stable)	2m 8s
cross (aarch64-unknown-linux-gnu, 1.65.0)	3m 20s
cross (aarch64-unknown-linux-gnu, stable)	2m 3s
cross (powerpc-unknown-linux-gnu, 1.65.0)	3m 55s
cross (powerpc-unknown-linux-gnu, stable)	1m 54s
test (i686-unknown-linux-gnu, 1.65.0, sudo apt update && sudo apt install gcc-multilib)	16m 29s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	12m 39s
test (x86_64-unknown-linux-gnu, 1.65.0)	3m 7s
test (x86_64-unknown-linux-gnu, stable)	1m 56s
doc	15s
	55m 23s

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