docs: def _contiguous_groups(
          length: int,
          comparator: Callable[[int, int], bool]
  ) -> List[Tuple[int, int]]:
      """Splits range(length) into approximate equivalence classes.
  
      Args:
          length: The length of the range to split.
          comparator: Determines if two indices have approximately equal items.
  
      Returns:
          A list of (inclusive_start, exclusive_end) range endpoints. Each
          corresponds to a run of approximately-equivalent items.
      """
      result = []
      start = 0
      while start < length:
          past = start + 1
          while past < length and comparator(start, past):
              past += 1
          result.append((start, past))
          start = past
      return result