Function mask_iou

tests/test_visual_only_compare.cpp:17–27

#include <vector>

static float mask_iou(const sam3_mask& a, const sam3_mask& b) {
    if (a.width != b.width || a.height != b.height) return 0.0f;
    int inter = 0, uni = 0;
    for (int i = 0; i < (int)a.data.size(); ++i) {
        bool fa = a.data[i] > 127;
        bool fb = b.data[i] > 127;
        if (fa && fb) inter++;
        if (fa || fb) uni++;
    }
    return uni > 0 ? (float)inter / uni : 1.0f;
}

static int count_fg(const sam3_mask& m) {
    int n = 0;