Remove `Arrange::arrange_core` #360

Job	Run time
test mdBook	51s
cargo test on ubuntu, rust stable	1m 10s
cargo test on ubuntu, rust 1.78	1m 3s
cargo test on macos, rust stable	1m 0s
cargo test on macos, rust 1.78	1m 24s
cargo test on windows, rust stable	2m 49s
cargo test on windows, rust 1.78	1m 41s
	9m 58s

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