add center calculation to segmentation workflow

when the segmentation mask is written to the spatialdata object the centers file for that mask is also generated. This not only tracks unique cell_ids but also their location for easier visualization

see #42

src/scportrait/pipeline/segmentation/segmentation.py

@@ -310,12 +310,14 @@ def _save_segmentation_sdata(self, labels, classes, masks=None):
                 self.filehandler._write_segmentation_sdata(
                     labels[ix], self.nuc_seg_name, classes=classes, overwrite=self.overwrite
                 )
+                self.filehandler._add_centers(self.nuc_seg_name, overwrite=self.overwrite)
 
             if "cytosol" in masks:
                 ix = masks.index("cytosol")
                 self.filehandler._write_segmentation_sdata(
                     labels[ix], self.cyto_seg_name, classes=classes, overwrite=self.overwrite
                 )
+                self.filehandler._add_centers(self.cyto_seg_name, overwrite=self.overwrite)
 
     def save_map(self, map_name):
         """Saves newly computed map.