Fix classifier cloning and reset in chunk processing

This commit fixes an issue in the chunk processing logic where the wrong classifier instance was being reset and used for code generation. A local clone of the classifier is now created and used to ensure correct behavior during dereplication.

pkg/obichunk/chunk_on_disk.go

@@ -110,6 +110,7 @@ func ISequenceChunkOnDisk(iterator obiiter.IBioSequence,
 	log.Infof("Data splitted over %d batches", nbatch)
 
 	go func() {
+		localClassifier := uniqueClassifier.Clone()
 
 		for order, file := range fileNames {
 			iseq, err := obiformats.ReadSequencesFromFile(file)
@@ -121,7 +122,7 @@ func ISequenceChunkOnDisk(iterator obiiter.IBioSequence,
 			if dereplicate {
 				u := make(map[string]*obiseq.BioSequence)
 				var source string
-				uniqueClassifier.Reset()
+				localClassifier.Reset()
 
 				for iseq.Next() {
 					batch := iseq.Get()
@@ -129,8 +130,8 @@ func ISequenceChunkOnDisk(iterator obiiter.IBioSequence,
 
 					for _, seq := range batch.Slice() {
 						// Use composite key: sequence + categories
-						code := uniqueClassifier.Code(seq)
-						key := uniqueClassifier.Value(code)
+						code := localClassifier.Code(seq)
+						key := localClassifier.Value(code)
 						prev, ok := u[key]
 						if ok {
 							prev.Merge(seq, na, true, statsOn)