Function format_psi_avg_cell 

pub fn format_psi_avg_cell(
    baseline: Option<u16>,
    candidate: Option<u16>,
) -> String

Render a baseline→candidate→delta cell for a PSI average field. baseline and candidate are centi-percent (0..=10000 covering 0.00..=100.00 %); the cell renders each as N.NN% and computes a signed delta (+|-D.DD%). Mirrors cgroup_cell’s structure but does NOT route through the auto-scale ladder — a pressure percentage is dimensionless and topping out at 100 means there’s nothing to scale.