UI: Ability to load pre-trained model

[melisande-c]

Problem

Users can save their model, but then there is no way to load a model. This would be useful for applying a model to similar data to what it was trained on.

Potential solution

A button to load a pre-trained model. There is already a placeholder but it hasn't been implemented.

https://github.com/CAREamics/careamics-napari/blob/c456c4b7c664566f5568db00ac12e0b362a749d8/src/careamics_napari/widgets/magicgui_widgets.py#L54-L63

[jdeschamps]

Now I remember, why this is there and not implemented.

The fine-tuning of models in CAREamics makes me a bit uneasy, because the plugin may cause the training to continue on the same overall dataset, but with different train/val split causing data leak.

So my original thought was to only allow loading models in a prediction plugin, which I never had the time to get back to! So this would be more linked to #7. (unless we do want that feature in the training plugin).