Use `hashbrown::HashTable` instead of `RawTable` #405

Job	Run time
Check MSRV and minimal-versions	1m 32s
clippy	15s
miri	4m 44s
nostd_build (1.63.0, thumbv6m-none-eabi)	1m 13s
nostd_build (stable, thumbv6m-none-eabi)	11s
tests (1.63.0)	1m 45s
tests (stable, arbitrary)	34s
tests (stable, quickcheck)	45s
tests (stable, rayon)	45s
tests (stable, rustc-rayon)	41s
tests (stable, serde)	40s
tests (stable, borsh)	34s
tests (stable, std)	33s
tests (beta)	35s
tests (nightly, test build benchmarks)	38s
Success	1s
	15m 26s

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