Function xnuma_compute_rates 

pub(crate) fn xnuma_compute_rates(
    duty_sums: &[f64],
    allocs: &[usize],
) -> XnumaRates

Compute water-fill migration rates for a single layer.

Finds the equalization ratio (water line) across all nodes, then computes per-(src, dst) migration rates proportional to each source’s surplus and each destination’s share of total deficit.