ecdsa

ecdsa: use `MulByGeneratorVartime` for public key recovery (#1410) #2786

Job	Run time
no_std (wasm32-unknown-unknown, 1.85.0)	1m 7s
test (stable)	31s
no_std (wasm32-unknown-unknown, stable)	1m 5s
no_std (thumbv7em-none-eabi, 1.85.0)	1m 6s
no_std (thumbv7em-none-eabi, stable)	1m 8s
test (1.85.0)	35s
	5m 32s

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