ctutils: impl `From<u8>` for `Choice` #121

Job	Run time
test (stable)	18s
test-careful	55s
build (1.85.0, wasm32-unknown-unknown)	16s
build (1.85.0, thumbv7em-none-eabi)	13s
build (stable, thumbv7em-none-eabi)	8s
build (stable, wasm32-unknown-unknown)	11s
test (1.85.0)	16s
test-miri (s390x-unknown-linux-gnu)	57s
test-miri (x86_64-unknown-linux-gnu)	40s
minimal-versions / minimal-versions	22s
	4m 16s

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