Refactor compression_core::util #514

Job	Run time
cargo test --shallow-minimal-versions	1m 28s
cargo test (stable, x86_64-pc-windows-msvc, windows-latest)	2m 27s
cargo test (stable, x86_64-unknown-linux-gnu, ubuntu-latest)	1m 21s
cargo test (stable, i686-unknown-linux-gnu, ubuntu-latest)	1m 23s
cargo test (stable, i686-pc-windows-msvc, windows-latest)	2m 22s
cargo test (stable, x86_64-apple-darwin, macos-latest)	1m 27s
cargo test minimal-versions	1m 40s
cargo hack check --feature-powerset --features tokio	2m 53s
cargo hack check --feature-powerset --features futures-io	3m 11s
cargo check --all-targets --feature-powerset --features futures-io	5m 17s
cargo check --all-targets --feature-powerset --features tokio	6m 3s
Exhaustive tests pass	2s
	29m 34s

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