raster_highest_score always returns the argmax cell, which lands on
noise when the loop has no crystal. Add a grid-wide weakness guard:
when max(spots_low_res) < min_low_res_spots OR max(spots_indexed) <
min_spots_indexed, return a CenterOfMassModel at the geometric grid
centre instead of collecting at a noisy cell. Thresholds are tunable
parameters (defaults 10.0 and 1).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>