Fix loaded data order bug when resuming from epoch >= 1
Author: ngazagna-qc
Pull request: yes

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Fixes #40690

Only 1 line added as described in the original issue.

Question: should we transform https://github.com/ngazagna-qc/transformers/blob/fix-data-order-resumed-epoch/reproduce_wrong_resumed_epoch.py into a test?

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Comments:
Hi @zach-huggingface @SunMarc : I am just following up on this bug and the proposed fix. It’s a one-line change with a reproducible example, and I’d love to help get it merged if possible. Let me know if you have any question :) 

Thanks a lot!

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_40691). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

Hi @SunMarc , Thanks for your feedback. Sure, let me check the tests and try to implement one to spot and check the correction of the bug. I will probably work on it tomorrow.

@SunMarc, I think we are close to be able to merge this PR:
- I updated the trainer under the `if steps_trained_in_current_epoch > 0:` condition as we discussed
- I wrote the test in `tests/trainer/test_trainer.py::TrainerIntegrationTest::test_resume_batch_order`
- I confirmed that without the fix, the test fails, with the fix, the test passes. 

One can run `pytest -v -s tests/trainer/test_trainer.py::TrainerIntegrationTest::test_resume_batch_order` to see the output and understand better the issue.

I tried to follow the contribution guidelines but I am not super familiar with the commands to run to format the code. Let me know if anything more is needed :)


Hello @SunMarc , just a quick follow-up after 2 weeks :) I hope my updates are good enough now !

make sure to rebase correctly, the diff is huge right now 

> make sure to rebase correctly, the diff is huge right now

I did reset from main. Let me know if anything else is due.

Hi @SunMarc , I believe the rebase on main is correct now 

@SunMarc to reproduce:
```shell
git clone https://github.com/ngazagna-qc/transformers.git
cd transformers
uv venv .my-env
source .my-env/bin/activate
uv pip install -e ".[torch,sentencepiece,tokenizers,vision,integrations,timm,torch-vision,codecarbon,accelerate,video,num2words,mistral-common,chat_template,testing,quality,ja,sklearn,modelcreation]"
git checkout pr-fix-data-order-resumed-epoch
pytest tests/trainer/test_trainer.py::TrainerIntegrationTest::test_resume_batch_order -v -s
```

Let me know if I can help. I hope we are very close to merging.

Hello, I just rebased to make it up to date @SunMarc and check if tests pass

@SunMarc I think I am done with the updates :)