perf: reduce serialization

Author: proost

kll/items_sketch.go

@@ -593,8 +593,11 @@ func (s *ItemsSketch[C]) currentSerializedSizeBytes() (int, error) {
 		}
 		totalBytes = _DATA_START_ADR_SINGLE_ITEM + v
 	} else if tgtStructure == _COMPACT_FULL {
-
-		totalBytes = _DATA_START_ADR + s.getLevelsArrSizeBytes(tgtStructure) + s.getMinMaxSizeBytes() + s.getRetainedItemsSizeBytes()
+		retainedSize := 0
+		for i := s.levels[0]; i < s.levels[s.numLevels]; i++ {
+			retainedSize += s.serde.SizeOf(s.items[i])
+		}
+		totalBytes = _DATA_START_ADR + s.getLevelsArrSizeBytes(tgtStructure) + s.getMinMaxSizeBytes() + retainedSize
 	} else { //structure = UPDATABLE
 		return 0, fmt.Errorf("updatable serialization not implemented")
 	}
@@ -669,10 +672,6 @@ func (s *ItemsSketch[C]) getRetainedItemsByteArr() []byte {
 	return s.serde.SerializeManyToSlice(retArr)
 }
 
-func (s *ItemsSketch[C]) getRetainedItemsSizeBytes() int {
-	return len(s.getRetainedItemsByteArr())
-}
-
 func (s *ItemsSketch[C]) setupSortedView() error {
 	if s.sortedView == nil {
 		sView, err := newItemsSketchSortedView[C](s)