Function breakdown_chart 

pub fn breakdown_chart(
    periods: &[BreakdownPeriodView],
    opts: BreakdownChartOpts,
) -> ChartSpec

Breakdown chart. Two shapes depending on whether the breakdown has period grouping:

• With periods (len > 1, or the single label is non-empty): x = period label, one series per top-N tag value.
• Flat (single period, empty label — meaning no period_grouping): x = tag value, a single series.