Breaking: Adapt coreutils dev file structure #651

Job	Run time
GNU test suite	2m 22s
cargo check (windows-latest)	51s
cargo check (macOS-latest)	21s
cargo clippy -- -D warnings (ubuntu-latest)	21s
cargo fmt --all -- --check	5s
cargo clippy -- -D warnings (windows-latest)	1m 9s
cargo clippy -- -D warnings (macOS-latest)	19s
Code Coverage (macos-latest, macos)	1m 58s
cargo check (ubuntu-latest)	26s
Code Coverage (ubuntu-latest, unix)	1m 37s
cargo test (ubuntu-latest)	19s
cargo test (macOS-latest)	35s
Code Coverage (windows-latest, windows)	3m 39s
cargo test (windows-latest)	1m 39s
	15m 41s

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