Return distances from GCP minimization

[mraspaud]

This PR returns gcp distances for the caller to have a measure of improvement.

• Closes #xxxx
• Tests added
• Fully documented

[mraspaud]

I'm realising this might no be the cleanest solution, we should probably return the distances instead.
Fixed

[codecov]

Codecov Report

❌ Patch coverage is 97.56098% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.58%. Comparing base (9159f20) to head (0a7ede2).
⚠️ Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
pyorbital/geoloc_avhrr.py	95.83%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #192      +/-   ##
==========================================
+ Coverage   89.49%   89.58%   +0.09%     
==========================================
  Files          17       17              
  Lines        2750     2784      +34     
==========================================
+ Hits         2461     2494      +33     
- Misses        289      290       +1     

Flag	Coverage Δ
unittests	89.58% <97.56%> (+0.09%)	⬆️

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[coveralls]

coverage: 89.543% (+0.09%) from 89.451%
when pulling 0a7ede2 on mraspaud:add-threshold-for-minimization
into 795c002 on pytroll:main.