docstr: Returns a collection with element in the correct format.
code: def bound_contributions(
      self, col, params, backend, report_generator, aggregate_fn
  ):
      """Returns a collection with element in the correct format."""
      return backend.map_tuple(
          col,
          lambda pid, pk, val: ((pid, pk), aggregate_fn(val)),
          "Apply aggregate_fn",
      )
  
file_path: pipelinedp/analysis/contribution_bounders.py
imports: from pipeline_dp import contribution_bounders
  from pipeline_dp import sampling_utils
label_desc: Use image node_id 1 for calling the NoOpContributionBounder obj's underlying member method code with example usage: obj.bound_contributions(col, params, backend, report_generator, aggregate_fn) and returns: backend