Function resolve_rust_use 

pub fn resolve_rust_use(
    use_path: &str,
    source_file: &str,
    project_root: &Path,
) -> Option<PathBuf>

Resolve a Rust use path to a file path relative to the project root.

source_file is relative to project_root (e.g., “astmap-core/src/db/mod.rs”). Returns an absolute path, or None for external crate imports.