Rust

Fix `Bump::shrink` illegal copies #187

Job	Run time
valgrind	1m 13s
miri	2m 1s
build (stable, --features collections,boxed)	39s
benches	20s
build (beta, --features collections,boxed)	39s
build (1.65.0, --features collections,boxed)	3m 36s
build (nightly, --all-features)	40s
build (stable, --no-default-features)	28s
	9m 36s

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