Revert "[FSDP Optim State] Remove checkpoint prefix (#80480)"
This reverts commit 04c50fec1ceec5b2d78934921f1cb366ff3fac81.
Reverted https://github.com/pytorch/pytorch/pull/80480 on behalf of https://github.com/suo due to Broke master https://hud.pytorch.org/pytorch/pytorch/commit/04c50fec1ceec5b2d78934921f1cb366ff3fac81, the test failures were not unrelated
