docs: def get_cds_seq_for_transcript(self, transcript_id):
          """ obtain the sequence for a transcript from ensembl
          """
          
          headers = {"content-type": "text/plain"}
          
          self.attempt = 0
          ext = "/sequence/id/{}?type=cds".format(transcript_id)
          
          return self.ensembl_request(ext,  headers)