zeroize: feature-gate AVX-512 under `simd`; MSRV 1.60 (#1073) #1663

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	48s
build (1.65.0, wasm32-unknown-unknown)	47s
build (stable, thumbv7em-none-eabi)	45s
build (stable, wasm32-unknown-unknown)	9s
test (1.65.0)	48s
test (stable)	37s
minimal-versions / minimal-versions	23s
	4m 17s

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