[FSDP] ufmt `flat_param.py`, `flatten_params_wrapper.py` (#83664)
I think we can move FSDP code to start using ufmt (https://ufmt.omnilib.dev/en/stable/) to unify formatting across developers. ufmt is the recommended formatter for PyTorch's Python code. If we have consensus, I can ufmt all of the FSDP code in follow-ups.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83664
Approved by: https://github.com/rohan-varma
