Function copy_file 

pub fn copy_file<F>(
    source: &Path,
    target: &Path,
    on_progress: F,
) -> Result<CopyResult, CopyError>
where
    F: Fn(&CopyProgress),

Copy a single file with progress callback.

Only copies if target doesn’t exist.

Arguments

• source - Source file path
• target - Target file path
• on_progress - Callback for progress updates

Errors

• If the copy operation fails