Add explicit `zeroize` features (#539) #995

Job	Run time
build (1.81.0, thumbv7em-none-eabi)	18s
test (1.81.0)	48s
build (1.81.0, wasm32-unknown-unknown)	23s
test (stable)	42s
build (stable, thumbv7em-none-eabi)	11s
build (stable, wasm32-unknown-unknown)	2m 6s
minimal-versions / minimal-versions	1m 33s
	6m 1s

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