Poc to use safetensors
# What does this PR do?

This PR introduces the necessary code changes to use safetensors weight file as a primary source.
Thank you for being verified!<|||||>_The documentation is not available anymore as the PR was closed or merged._<|||||>This looks so clean !<|||||>Opened Hub Pull requests to convert the following weights:
- https://huggingface.co/roberta-base/discussions/3
- https://huggingface.co/roberta-large/discussions/1
- https://huggingface.co/gpt2/discussions/6
- https://huggingface.co/Jean-Baptiste/camembert-ner/discussions/1
- https://huggingface.co/openai/clip-vit-large-patch14/discussions/5

^will merge the 3 canonical ones to be able to test easily<|||||>note that you can also test from un-merged Hub PRs, you just have to pass the `refs/pr/:id` as a `revision`, for instance for gpt2:

```python
model = AutoModelForCausalLM.from_pretrained("gpt2", revision="refs/pr/6")
```
