Tests

Parallel compactions for Leveled compaction #455

Job	Run time
cross (aarch64-unknown-linux-gnu)	2m 37s
test (stable, ubuntu-latest)	2m 16s
test (stable, windows-latest)	4m 4s
cross (aarch64-unknown-linux-musl)	3m 22s
test (stable, macos-latest)	1m 43s
cross (i686-unknown-linux-gnu)	2m 14s
test (1.74.0, ubuntu-latest)	2m 17s
cross (powerpc64-unknown-linux-gnu)	2m 37s
test (1.74.0, windows-latest)	4m 21s
cross (riscv64gc-unknown-linux-gnu)	2m 11s
test (1.74.0, macos-latest)	2m 44s
	30m 26s

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