Blob detection finds fewer blobs

[tibuch]

Since the latest release fewer blobs are detected for the same scale factor.

I think this is related to wrong normalization here:

faim-ipa/src/faim_ipa/detection/blobs.py

Line 72 in 06f1b7c

* (np.mean(sigma) / np.mean(sigmas[0])) ** 2

np.mean(sigmas[0]) should be np.mean([axial_sigma, lateral_sigma, lateral_sigma])