input: def calculate_rRNA_percentage(gtf_file: str, htseq_counts_file: str) -> str:
      """
      Calculates the percentage of transcripts mapping to rRNA and MT genes from the given HTseq_counts file and GTF file.
      It produces a summary output file named "HTseq_counts_file_rRNAmtRNACounts.txt" containing the counts and percentages.
  
      >>> calculate_rRNA_percentage('/path/to/GTF/file', '/path/to/HTseq_counts/file')
      'Summary output file: /path/to/HTseq_counts/file_rRNAmtRNACounts.txt'
      """
output:     rRNA_genes = set()
      MT_genes = set()
  
      with open(gtf_file, 'r') as gtf:
          for line in gtf:
              if line.startswith('#'):
                  continue
              fields = line.strip().split('\t')
              if fields[2] == 'gene':
                  attributes = fields[8].split(';')
                  gene_name = None
                  gene_type = None
                  for attr in attributes:
                      if 'gene_name' in attr:
                          gene_name = attr.split('"')[1]
                      if 'gene_biotype' in attr:
                          gene_type = attr.split('"')[1]
                  if gene_type == 'rRNA':
                      rRNA_genes.add(gene_name)
                  elif gene_type == 'Mt_rRNA':
                      MT_genes.add(gene_name)
  
      rRNA_count = 0
      MT_count = 0
      total_count = 0
  
      with open(htseq_counts_file, 'r') as htseq:
          for line in htseq:
              if line.startswith('__'):
                  continue
              gene_name, count = line.strip().split('\t')
              count = int(count)
              total_count += count
              if gene_name in rRNA_genes:
                  rRNA_count += count
              elif gene_name in MT_genes:
                  MT_count += count
  
      rRNA_percentage = (rRNA_count / total_count) * 100
      MT_percentage = (MT_count / total_count) * 100
  
      output_file = htseq_counts_file + '_rRNAmtRNACounts.txt'
      with open(output_file, 'w') as out:
          out.write(f"Total counts: {total_count}\n")
          out.write(f"rRNA counts: {rRNA_count} ({rRNA_percentage:.2f}%)\n")
          out.write(f"MT counts: {MT_count} ({MT_percentage:.2f}%)\n")
  
      return f'Summary output file: {output_file}'