Import structure & first three model refactors (#31329)
* Import structure & first three model refactors
* Register -> Export. Export all in __all__. Sensible defaults according to filename.
* Apply most comments from Amy and some comments from Lucain
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>
Co-authored-by: Lucain Pouget <lucainp@gmail.com>
* Style
* Add comment
* Clearer .py management
* Raise if not in backend mapping
* More specific type
* More efficient listdir
* Misc fixes
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Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>
Co-authored-by: Lucain Pouget <lucainp@gmail.com>
