Function sparkline 

pub fn sparkline(values: &[f64]) -> String

A sparkline, scaled to the series’ own range.

Per-series scaling is the only useful choice: an install benchmark at 100M instructions and a startup one at 7M share no axis, and a shared one would flatten every series but the largest into a straight line.

A flat series renders mid-height rather than at the floor. All-▁ reads as “bottomed out” when it actually means “did not move”, which for a deterministic metric is the best possible outcome and should not look like the worst.