Function pio_branch_charging 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_branch_charging(
    net: *const PioNetwork,
    g_fr: *mut f64,
    b_fr: *mut f64,
    g_to: *mut f64,
    b_to: *mut f64,
    cap: usize,
) -> usize

Write the branch terminal charging table as parallel arrays, each up to cap entries, and return the total branch count. Columns are p.u.