Fix slicing for 0-dim param

[SunMarc]

What does this PR do?

This PR fixes a slicing issue that we have with 0-dim tensors (both with param from bin file and safetensors pyslice). We can do [:] but [...] works instead. Thx fxmarty-amd for finding this solution.

cc @DN6

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[hlky]

Also can't slice 0-dim tensors. See CI from diffusers with MusicLDM and AudioLDM2 which use ClapModel from transformers. https://github.com/huggingface/diffusers/actions/runs/13714387592/job/38359634948?pr=10997

model = ClapModel(
  (text_model): ClapTextModel(
    (embeddings): ClapTextEmbeddings(
      (word_embeddings): Embedding(100...eatures=16, bias=True)
    (activation): ReLU()
    (linear2): Linear(in_features=16, out_features=16, bias=True)
  )
)
state_dict = {'audio_model.audio_encoder.batch_norm.bias': tensor(..., device='meta', size=(8,)), 'audio_model.audio_encoder.batch_...ice='meta', size=(8,)), 'audio_model.audio_encoder.batch_norm.running_var': tensor(..., device='meta', size=(8,)), ...}
...
>               param = param[:]
E               IndexError: slice() cannot be applied to a 0-dim tensor.

[SunMarc]

did you launch the tests if this specific pr ?
For safetensors file, param is a PySlice object. This is why we need to do param = param[:]
param = file_pointer.get_slice(serialized_param_name)

[SunMarc]

okay it's the same as here #36372 (comment)