Function diff_paths 

pub fn diff_paths(
    old_path: &str,
    new_path: &str,
    options: Option<&DiffOptions>,
) -> Result<Vec<DiffResult>>

Unified diff function for diffx (path-based entry point)

This is the main entry point that handles both files and directories.

• File vs File: Regular file comparison
• Directory vs Directory: Requires –recursive flag, otherwise error
• File vs Directory: Returns error