Function compute_qc_stack 

pub fn compute_qc_stack(
    stack: &SparseIoStack,
    cfg: &QcConfig,
    block_size: Option<usize>,
) -> Result<QcReport>

Modality-agnostic cell QC for a SparseIoStack: per-cell n_genes / total_counts are summed across all member modalities (mirrors senna gem’s “a cell rich in any one modality is kept”). Mito/ribo and feature-axis QC are skipped on stacks (row names are per-modality).