save space when converting hf model to megatron model.
Author: flower-with-safe
Pull request: yes

# What does this PR do?

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Fixes #25911 

when save megatron models, clone the tensor to avoid saving the original tensor.

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Yes

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@ArthurZucker 

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Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_25950). All of your documentation changes will be reflected on that endpoint.

you are right, I add the LM head. But I  think layer norm doesn't need this method， they are replicated across the tensor paralledl group.
@ArthurZucker 

Thanks! Looks good to me 😉