Function evaluate_density_cpu 

pub fn evaluate_density_cpu(
    basis: &BasisSet,
    density: &DMatrix<f64>,
    params: &GridParams,
) -> Vec<f64>

Evaluate electron density ρ(r) = Σ_{μν} P_{μν} φ_μ(r) φ_ν(r) on a 3D grid.