[loading] Fix base_model_prefix issues in conversions (#46067)
* Improve interaction between scoped match and base_model_prefix
* simplify
* style
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Co-authored-by: yonigozlan <yoni.gozlan@huggingface.co>
Co-authored-by: Yoni Gozlan <74535834+yonigozlan@users.noreply.github.com>