class_docstr: Adds an id to the time series. For rolling test sets
  the time series that are an extension of each other have the same id.
code: def __call__(self, items: List[Item]) -> List[Item]:
      assert (not self.required_length) or (
          not len(items) % self.required_length
      ), "Either no length specified or number of times series is a multiple of specified length."
      self.required_length = self.required_length or len(items)
      it_ids = cycle(range(self.required_length))
      for item in items:
          item[FieldName.ITEM_ID] = next(it_ids)
      return items
  
file_path: gluonts/src/gluonts/nursery/few_shot_prediction/src/meta/datasets/preprocessing/transform.py
imports: from abc import ABC, abstractmethod
  import json
  from itertools import cycle
  from pathlib import Path
  from typing import List, Optional, Any, Dict
  from gluonts.dataset.field_names import FieldName
  from .filters import Filter
label_desc: Use image node_id 2 for calling the ItemIDTransform obj's underlying member method code with example usage: obj.__call__(items) and returns: items