Clarification: SigLIP Image Transform

Thanks for open-sourcing the SigLIP models!

Clarification question: in the demo IPython notebook, the image transform function has the form `pp_img = pp_builder.get_preprocess_fn(f'resize({RES})|value_range(-1, 1)')`.

Looking at the code [here](https://github.com/google-research/big_vision/blob/main/big_vision/pp/ops_image.py#L64), this seems to be resizing an image to `RES x RES` (warping aspect ratio).

Is this the expected behavior? Were the SigLIP models trained with this transform (aspect ratio warping)?

Start with the demo IPython notebook and the linked implementation in pp/ops_image.py, especially the resize operation. Verify whether the transform warps aspect ratio and whether it matches the SigLIP training setup; done means documenting a definitive answer to both questions.

Written by the indexing model from the issue text.