convert : allow conversion of Mistral HF models (#6144)

convert : allow conversion of Mistral HF models (#6144)

* Allow conversion of Mistral HF models

* Homogenize Llama, Mistral, Mixtral under the same entry.

* Fix tokenizer, permute tensors

* Use sentencepiece tokenizer, or fall back to hfft.

* convert-hf : small fix for mypy

* convert-hf : fix duplicated block_count

* convert-hf : add vocab size to metadata

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Co-authored-by: Jared Van Bortel <redacted>