ecdsa

ecdsa: fix `clippy::missing_errors_doc` lints #2787

Job	Run time
test (stable)	38s
no_std (thumbv7em-none-eabi, stable)	1m 2s
test (1.85.0)	35s
no_std (wasm32-unknown-unknown, stable)	1m 9s
no_std (wasm32-unknown-unknown, 1.85.0)	1m 6s
no_std (thumbv7em-none-eabi, 1.85.0)	1m 8s
	5m 38s

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