Add inactive AVX-512 encode prototype #39

Job	Run time
Format, lint, test, and audit	19s
Platform tests (ubuntu-latest)	19s
Platform tests (windows-latest)	38s
no_std target build (x86_64-unknown-linux-gnu)	16s
no_std target build (wasm32-unknown-unknown)	20s
Miri	2m 2s
no_std target build (thumbv7em-none-eabihf)	20s
Platform tests (macos-latest)	24s
no_std target build (x86_64-unknown-freebsd)	16s
no_std target build (aarch64-unknown-linux-gnu)	18s
	5m 12s

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