zeroizing: add `repr(transparent)` to `Zeroizing` (#1253) #1948

Job	Run time
test (stable)	17s
build (stable, thumbv7em-none-eabi)	16s
test (1.85.0)	18s
build (stable, wasm32-unknown-unknown)	18s
build (1.85.0, wasm32-unknown-unknown)	18s
build (1.85.0, thumbv7em-none-eabi)	15s
minimal-versions / minimal-versions	30s
	2m 12s

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