Function prepare_kde_data 

pub fn prepare_kde_data<T: AsRef<str>>(
    lf: &LazyFrame,
    columns: &[T],
    bandwidth_factor: f64,
    range: ValueRange,
    sampling: &ChartSampling,
) -> Result<KdeData>

Prepare KDE data for one or more numeric columns. Uses a single read for all columns.