* Register ModelOutput subclasses as supported torch.utils._pytree nodes
Fixes#25357 where DDP with static_graph=True does not sync gradients when calling backward() over tensors contained in ModelOutput subclasses
* Add test for torch pytree ModelOutput serialization and deserialization
* Split file_utils in several submodules
* Fixes
* Add back more objects
* More fixes
* Who exactly decided to import that from there?
* Second suggestion to code with code review
* Revert wront move
* Fix imports
* Adapt all imports
* Adapt all imports everywhere
* Revert this import, will fix in a separate commit