Include chat_template_kwargs in apply_chat_template

[cmpatino]

What does this PR do?

This pull request updates the apply_chat_template function in trl/data_utils.py to read the chat_template_kwargs from a dataset.

The version in main ignores the chat_template_kwargs and degrades the performance when setting chat template settings through a dataset. We ran tests using the DPOTrainer on the it-SFT checkpoint from HuggingFaceTB/SmolLM3-3B-checkpoints and saw improvements of ~10 points in AIME25 and GPQA with this fix.

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[lewtun]

Thanks for the fix, LGTM!

I wonder if it makes sense to also include a regression test, but I'll defer to @qgallouedec's judgement on that

[edbeeching]

Thanks for porting this over

[qgallouedec]

thanks!

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