Function fmt_up_to_n_elements 

fn fmt_up_to_n_elements<E, F>(
    elements: &[E],
    n: usize,
    f: &mut Formatter<'_>,
    format_element: F,
) -> Result
where
    F: Fn(&E, &mut Formatter<'_>) -> Result,

helper to format an array of up to N elements