Serialization improvement

[casenave]

Current serialization uses pydantic and pickle, which poses security threats, cf https://arjancodes.com/blog/python-pickle-module-security-risks-and-safer-alternatives/

For model weights, Hugging Face has developped safetensors: https://huggingface.co/docs/safetensors/index

Is it possible de update the serialization to be fully secure ? The difficulity here is the that the cgns trees contain numpy arrays, whcih prevents straightforward json serialization