Rust

Fix `Bump::shrink` illegal copies #188

Job	Run time
valgrind	1m 7s
benches	22s
build (stable, --features collections,boxed)	38s
miri	1m 59s
build (beta, --features collections,boxed)	42s
build (1.65.0, --features collections,boxed)	3m 34s
build (nightly, --all-features)	41s
build (stable, --no-default-features)	28s
	9m 31s

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