pytorch

23ee6757 - [Checkpoint][2D][4/N] Add nested_dict for distributed checkpoint to core distributed (#89537)

[Checkpoint][2D][4/N] Add nested_dict for distributed checkpoint to core distributed (#89537) This PR moves nested_dict and its test to torch.distributed.checkpoint. This is a pre-req for enabling 2D checkpoint. This provides the functionality to flatten a nested dict and unflatten a flattened dict. Docstring will be added in the following PR. Pull Request resolved: https://github.com/pytorch/pytorch/pull/89537 Approved by: https://github.com/fduwjj, https://github.com/wanchaol