block-buffer: add optional Zeroize implementation #454

Job	Run time
aarch64 (aarch64-unknown-linux-gnu, 1.60.0)	5m 49s
build (1.60.0, armv7a-none-eabi)	4m 57s
aarch64 (aarch64-unknown-linux-gnu, stable)	48s
build (1.60.0, thumbv7em-none-eabi)	4m 13s
build (1.60.0, wasm32-unknown-unknown)	4m 7s
build (stable, armv7a-none-eabi)	18s
cross (powerpc-unknown-linux-gnu, 1.60.0)	5m 32s
cross (powerpc-unknown-linux-gnu, stable)	43s
build (stable, thumbv7em-none-eabi)	15s
build (stable, wasm32-unknown-unknown)	13s
test (i686-unknown-linux-gnu, ubuntu-latest, 1.60.0, sudo apt update && sudo apt install gcc-mult...	4m 39s
test (i686-unknown-linux-gnu, ubuntu-latest, stable, sudo apt update && sudo apt install gcc-mult...	56s
test (x86_64-unknown-linux-gnu, ubuntu-latest, 1.60.0)	4m 21s
test (x86_64-unknown-linux-gnu, ubuntu-latest, stable)	18s
test (x86_64-apple-darwin, macos-latest, 1.60.0)	6m 20s
test (x86_64-apple-darwin, macos-latest, stable)	39s
test (x86_64-pc-windows-msvc, windows-latest, 1.60.0)	7m 12s
test (x86_64-pc-windows-msvc, windows-latest, stable)	2m 9s
minimal-versions / minimal-versions	1m 10s
	54m 39s

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