ecdsa: use `MulByGeneratorVartime` for public key recovery (#1410) #244

Job	Run time
build (thumbv7em-none-eabi, 1.85.0)	17s
build (wasm32-unknown-unknown, 1.85.0)	18s
test (stable)	21s
build (wasm32-unknown-unknown, stable)	20s
build (thumbv7em-none-eabi, stable)	17s
test (1.85.0)	19s
	1m 52s

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