Zephon brings elastically deterministic data loading to TorchTitan

Zephon is a data loader that tokenizes, packs, shuffles, and mixes data inside the training job and keeps global batches identical across GPU counts.

In the authors' tests, a standard loader shifted DCLM Core v1 scores by up to 0.82 points depending on GPU count, while Zephon's spread was 0.05 points. The TorchTitan integration lets a run resume on a different number of GPUs from the same checkpoint.