fix: drop negative counter inc (#336)

Author: kwasniew

unleash-yggdrasil/src/impact_metrics/counter.rs

@@ -31,6 +31,9 @@ impl Counter {
     }
 
     fn inc_internal(&self, value: i64, labels: Option<&MetricLabels>) {
+        if value <= 0 {
+            return;
+        }
         let key = get_label_key(labels);
         self.values
             .entry(key)

unleash-yggdrasil/src/impact_metrics/registry.rs

@@ -225,6 +225,7 @@ mod tests {
         let lbls = labels(&[("foo", "bar")]);
         registry.inc_counter_with_labels("labeled_counter", 3, &lbls);
         registry.inc_counter_with_labels("labeled_counter", 2, &lbls);
+        registry.inc_counter_with_labels("labeled_counter", -1, &lbls); // dropped
 
         let metrics = registry.collect();
         let expected = CollectedMetric::new_counter(