ctutils: use signed `Cmov*` trait impls (#1282) #77

Job	Run time
test-miri (x86_64-unknown-linux-gnu)	40s
test-careful	53s
test (1.85.0)	15s
test (stable)	20s
test-miri (s390x-unknown-linux-gnu)	55s
minimal-versions / minimal-versions	21s
build (1.85.0, thumbv7em-none-eabi)	17s
build (stable, wasm32-unknown-unknown)	10s
build (stable, thumbv7em-none-eabi)	11s
build (1.85.0, wasm32-unknown-unknown)	14s
	4m 16s

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