zeroize: feature-gate AVX-512 under `simd`; MSRV 1.60 (#1073) #1643

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	55s
build (1.65.0, wasm32-unknown-unknown)	44s
test (1.65.0)	42s
build (stable, thumbv7em-none-eabi)	30s
test (stable)	21s
build (stable, wasm32-unknown-unknown)	23s
minimal-versions / minimal-versions	35s
	4m 10s

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