Add support of `CroppedImageServer`

[NicoKiaru]

Claude's recommendations, to which I totally agree :

This is doable but non-trivial. The cleanest approach:

1. First, inspect a QuPath project JSON that contains a CroppedImageServer to see the exact serialization format
2. Extend MinimalQuPathProject.ServerBuilderEntry with crop region fields
3. Create CroppedOpener following the PyramidizeOpener pattern
4. Create CroppedSetupLoader that wraps the inner SetupLoader and translates coordinates