Second attempt to fix issue #30: Classifier widget restarts

[jluethi]

• Pin pandrea (see Update to pandera >0.19.3 #45)

[jluethi]

The issue with #30 was having existing Annotation & Prediction layers. I now ensure that they get removed when using Load Classifier. Now that workflow appears to work robustly.

I noticed another issue in the Load Classifier flow though: The keybindings for e.g. switching classes stop working. The necessary section of code is run with the correct parameters as far as I can tell. Don't know why does keybindings aren't working in that section anymore.

[jluethi]

Also, I needed to pin numpy < 2 because of different test failures otherwise. Some related to np.string_ usage, others that I can't make sense of

[jluethi]

This PR now fixes a few things:

1. Handles translation in the layers correctly (also during annotation)
2. Improve behavior upon Load Classifier: It shouldn't be required anymore to restart napari in regular workflows
3. Right-click an annotation to remove it