Function select_keypoints_grid 

pub fn select_keypoints_grid(
    keypoints: &[Keypoint2],
    width: usize,
    height: usize,
    options: GridSelectionOptions,
) -> Result<Vec<Keypoint2>, VisionError>

Retains the strongest keypoints in each image cell.

Output is ordered by cell scan order, then decreasing response, with the input index as the deterministic tie breaker.