Add equals and hashcode implementation to KnownCardinalityUpperBound (#62930) (#63045)

server/src/main/java/org/elasticsearch/search/aggregations/CardinalityUpperBound.java

@@ -129,5 +129,18 @@ public abstract class CardinalityUpperBound {
         public <R> R map(IntFunction<R> mapper) {
             return mapper.apply(estimate);
         }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            if (o == null || getClass() != o.getClass()) return false;
+            KnownCardinalityUpperBound that = (KnownCardinalityUpperBound) o;
+            return estimate == that.estimate;
+        }
+
+        @Override
+        public int hashCode() {
+            return Integer.hashCode(estimate);
+        }
     }
 }