stack zeroization #1888

Job	Run time
build (1.85.0, thumbv7em-none-eabi)	18s
test (stable)	26s
test (1.85.0)	17s
build (stable, thumbv7em-none-eabi)	19s
build (stable, wasm32-unknown-unknown)	12s
build (1.85.0, wasm32-unknown-unknown)	16s
minimal-versions / minimal-versions	26s
	2m 14s

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