ecdsa: remove `OutputSize` bounds on `DigestPrimitive` (#774) #599

Job	Run time
test (1.71.0)	17s
build (thumbv7em-none-eabi, 1.71.0)	16s
test (stable)	17s
build (thumbv7em-none-eabi, stable)	8s
build (wasm32-unknown-unknown, 1.71.0)	14s
build (wasm32-unknown-unknown, stable)	9s
	1m 21s

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