Add support for `findmnt` #748

Job	Run time
cargo check (ubuntu-latest)	20s
cargo check (macOS-latest)	33s
cargo fmt --all -- --check	3s
Code Coverage (ubuntu-latest, unix)	54s
cargo check (windows-latest)	2m 32s
cargo clippy -- -D warnings (ubuntu-latest)	19s
Code Coverage (macos-latest, macos)	39s
cargo clippy -- -D warnings (macOS-latest)	26s
Code Coverage (windows-latest, windows)	37s
cargo test (ubuntu-latest)	30s
cargo clippy -- -D warnings (windows-latest)	2m 46s
cargo test (macOS-latest)	38s
cargo test (windows-latest)	38s
	10m 55s

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