Upgrade PyTorch to 2.7.1

[pquentin]

Following elastic/ml-cpp#2863, which was only applied to 9.x, not 8.x

[prodsecmachine]

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[edsavage]

LGTM

Note that this PyTorch version includes a fix for a CVE.

which resulted in Huggingface disabling the torch.load method for certain models in in version 4.51.

https://github.com/huggingface/transformers/blame/4884b6bf41f26eb4f894214dc3ae34f80dbed9dd/src/transformers/utils/import_utils.py#L1588

For this reason the Huggingface version was pinned to 4.50.3 in Eland (to ensure model upload still worked.) It should now be fine to upgrade Huggingface to a version later than 4.50.3

[pquentin]

Somehow I pushed the PyTorch upgrade in #810, so this is only about the transformers ugprade.