Improve integration of Cellpose detection in pipeline

Currently, we call Cellpose in QuPath projects via the cellpose extension.

This requires the manual installation of the extension for every user that needs the pipeline. It's unclear if this can be avoided (see Image.sc post).

It's maybe more efficient to run Cellpose detection before importing the images in QuPath. This would require importing the Cellpose segmentation objects in QuPath, which is currently not implemented.