docs: def find_last_timden_file(self):
          """
          ABINIT produces lots of out_TIM1_DEN files for each step and we need to find the lat
          one in order to prepare the restart or to connect other tasks to the structural relaxation.
  
          This function finds all the TIM?_DEN files in self and return a namedtuple (path, step)
          where `path` is the path of the last TIM?_DEN file and step is the iteration number.
          Returns None if the directory does not contain TIM?_DEN files.
          """
          regex = re.compile(r"out_TIM(\d+)_DEN(.nc)?$")
  
          timden_paths = [f for f in self.list_filepaths() if regex.match(os.path.basename(f))]
          if not timden_paths: return None
  
          # Build list of (step, path) tuples.
          stepfile_list = []
          for path in timden_paths:
              name = os.path.basename(path)
              match = regex.match(name)
              step, ncext = match.groups()
              stepfile_list.append((int(step), path))
  
          # DSU sort.
          last = sorted(stepfile_list, key=lambda t: t[0])[-1]
          return dict2namedtuple(step=last[0], path=last[1])