pub fn build_denested_partition_cells<FS, FL>(
a: f64,
b: f64,
score_breaks: &[f64],
link_breaks: &[f64],
score_span_at: FS,
link_span_at: FL,
) -> Result<Vec<DenestedPartitionCell>, String>where
FS: FnMut(f64) -> Result<LocalSpanCubic, String>,
FL: FnMut(f64) -> Result<LocalSpanCubic, String>,