docs: def last_sleep_breakdown(self):
          """Return durations of sleep stages for last complete session."""
          try:
              stages = self.intervals[1]['stages']
          except KeyError:
              return None
  
          breakdown = {'awake': 0, 'light': 0, 'deep': 0, 'rem': 0}
          for stage in stages:
              if stage['stage'] == 'awake':
                  breakdown['awake'] += stage['duration']
              elif stage['stage'] == 'light':
                  breakdown['light'] += stage['duration']
              elif stage['stage'] == 'deep':
                  breakdown['deep'] += stage['duration']
              elif stage['stage'] == 'rem':
                  breakdown['rem'] += stage['duration']
          return breakdown