clippy: fix warnings #428

Job	Run time
cargo check (ubuntu-latest)	19s
cargo test (ubuntu-latest)	42s
cargo test (windows-latest)	3m 29s
cargo check (windows-latest)	42s
cargo check (macOS-latest)	21s
cargo clippy -- -D warnings (macOS-latest)	19s
cargo test (macOS-latest)	1m 37s
cargo clippy -- -D warnings (windows-latest)	45s
cargo fmt --all -- --check	16s
cargo clippy -- -D warnings (ubuntu-latest)	18s
GNU test suite	3m 9s
Code Coverage (macos-latest, macos)	3m 7s
Code Coverage (windows-latest, windows)	6m 2s
Code Coverage (ubuntu-latest, unix)	1m 55s
	23m 1s

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