Fix unsoundness in `BucketBackend::shrink_to_fit` (#66) #164

Job	Run time
Test (ubuntu-latest)	39s
Test Memory Consumption (ubuntu-latest)	32s
Test (windows-latest)	2m 35s
Test Memory Consumption (windows-latest)	2m 27s
Test (macos-latest)	40s
Documentation	11s
Build (ubuntu-latest)	27s
Test Memory Consumption (macos-latest)	31s
Build (windows-latest)	49s
Formatting	12s
Build (macos-latest)	20s
Audit	9s
Clippy	17s
Coverage	4s
Miri	1m 32s
Outdated	10s
	11m 35s

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