code: def listext(self, ext, stream=sys.stdout):
          
          nodes_files = []
          for node in self.iflat_nodes():
              filepath = node.outdir.has_abiext(ext)
              if filepath:
                  nodes_files.append((node, File(filepath)))
  
          if nodes_files:
              print("Found %s files with extension `%s` produced by the flow" % (len(nodes_files), ext), file=stream)
  
              table = [[f.relpath, "%.2f" % (f.get_stat().st_size / 1024**2),
                        node.node_id, node.__class__.__name__]
                       for node, f in nodes_files]
              print(tabulate(table, headers=["File", "Size [Mb]", "Node_ID", "Node Class"]), file=stream)
  
          else:
              print("No output file with extension %s has been produced by the flow" % ext, file=stream)
docs: Print to the given `stream` a table with the list of the output files
          with the given `ext` produced by the flow.