zeroize: add unsafe `zeroize_flat_type` function (#1045) #1630

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	2m 44s
test (1.65.0)	2m 36s
test (stable)	16s
build (1.65.0, wasm32-unknown-unknown)	2m 39s
build (stable, thumbv7em-none-eabi)	9s
build (stable, wasm32-unknown-unknown)	10s
minimal-versions / minimal-versions	16s
	8m 50s

Provide feedback