Function cargo_automatic_target_directory 

pub fn cargo_automatic_target_directory<'a>(
    path: &'a str,
    root: &str,
) -> Option<&'a str>

Return the inventory directory for a flat potential automatic Cargo root.

This classifies source placement, not actual target membership or discovery policy.

assert_eq!(projectatlas_symbols::cargo_automatic_target_directory("src/bin/app.rs", ""), Some("src/bin"));
assert_eq!(projectatlas_symbols::cargo_automatic_target_directory("src/bin/app/main.rs", ""), None);