Function quantile_matrix_to_output 

pub fn quantile_matrix_to_output(
    qmat: &QuantileMatrix,
    quantile_levels: &[f32],
    median_idx: usize,
) -> ForecastOutput

Turn one forecast’s QuantileMatrix into a ForecastOutput, choosing the univariate (flat point/quantiles) or multivariate (variates: [...]) shape based on how many variates the matrix actually has.

quantile_levels[i] is the probability level for qmat[i]; median_idx is the row holding the point forecast (usually the index of level 0.5).