Function pio_switches 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_switches(
    net: *const PioNetwork,
    from: *mut i64,
    to: *mut i64,
    closed: *mut u8,
    thermal_rating: *mut f64,
    current_rating: *mut f64,
    pf: *mut f64,
    qf: *mut f64,
    pt: *mut f64,
    qt: *mut f64,
    cap: usize,
) -> usize

Write the switch table as parallel arrays, each up to cap entries, and return the total switch count. from/to are external bus ids.