fn auto_min_mask_runs(total_rows: usize, threshold: usize) -> Option<usize>Expand description
Returns the minimum normalized run count for which the Auto selection policy would prefer a mask to RLE.
Auto prefers masks when the average run length is strictly below threshold.
For positive thresholds and totals below usize::MAX, the first qualifying
run count is floor(total_rows / threshold) + 1.
Returns None when selectors are always preferred for a non-empty selection.
Callers handle empty selections separately.