Function read_subcell_accounts 

pub(crate) fn read_subcell_accounts<I>(
    skel: &BpfSkel<'_>,
    active_subcells: I,
) -> Result<HashMap<(usize, usize), Vec<subcell_account>>>
where
    I: IntoIterator<Item = (usize, usize)>,

Read the per-CPU accounting slots of active_subcells from BPF.