Refactor taxonomy handling and improve performance

This update introduces logic for handling embedded taxonomy, allowing users to specify taxonomy or extract it from sequences, while optimizing performance through reduced memory usage. It also adds batch reordering capabilities and implements comprehensive testing to ensure correct precedence rules and robust error handling for missing taxonomic paths.

pkg/obiiter/batchiterator.go

@@ -465,7 +465,9 @@ func (iterator IBioSequence) RebatchBySize(maxBytes int, maxCount int) IBioSeque
 
 	go func() {
 		order := 0
-		iterator = iterator.SortBatches()
+		// a local variable: reassigning the captured iterator would race with
+		// the IsPaired call below, made by the caller on the same variable
+		sorted := iterator.SortBatches()
 		buffer := obiseq.MakeBioSequenceSlice()
 		bufBytes := 0
 		source := ""
@@ -479,8 +481,8 @@ func (iterator IBioSequence) RebatchBySize(maxBytes int, maxCount int) IBioSeque
 			}
 		}
 
-		for iterator.Next() {
-			seqs := iterator.Get()
+		for sorted.Next() {
+			seqs := sorted.Get()
 			source = seqs.Source()
 			for _, s := range seqs.Slice() {
 				sz := s.MemorySize()