Add x,y coords and cell size in pixels to Nimbus final results

[Copilot]

Summary

Closes issue #57 by adding cell centroid coordinates (x, y) and cell size (area in pixels) to the Nimbus cell table output, making these spatial properties available for downstream analysis.

Changes

• src/nimbus_inference/utils.py:

  • Added 'area' to the regionprops_table properties in segment_mean() (centroid was already included)
  • In predict_fovs(), extracted centroid_x, centroid_y, and area columns from the regionprops output and added them to the per-FOV DataFrame

• tests/test_utils.py:

  • Updated expected column sets in test_predict_fovs to include centroid_x, centroid_y, and area

Output columns

The cell table now includes these additional columns:

Column	Description
centroid_x	X coordinate (column) of cell centroid in pixels
centroid_y	Y coordinate (row) of cell centroid in pixels
area	Cell size in pixels