[DLv2] Make graph `traverse` working with unhashable `DataPipe` (#80509)
Summary:
This Diff removes the requirement for `traverse` function that `DataPipe` needs to be hash-able. `traverse` function now is using `id` of `DataPipe` instance rather than `DataPipe` itself as the key for both `cache` and graph.
But, it requires the changes of type of `DataPipeGraph` from `Dict[DataPipe, "DataPipeGraph"]` to `Dict[int, Tuple[DataPipe, "DataPipeGraph"]]`.
Differential Revision: D37354153
Ref PR in TorchData: https://github.com/pytorch/data/pull/559
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80509
Approved by: https://github.com/VitalyFedyunin
