Added possibility to save results

[thuiop]

Closes #142

I still have to add utility functions for loading the saved results easily.

[codecov]

Codecov Report

Merging #148 (489af69) into main (d198d09) will increase coverage by 0.82%.
The diff coverage is 93.05%.

@@            Coverage Diff             @@
##             main     #148      +/-   ##
==========================================
+ Coverage   80.33%   81.15%   +0.82%     
==========================================
  Files          10       11       +1     
  Lines        1144     1215      +71     
==========================================
+ Hits          919      986      +67     
- Misses        225      229       +4     

Flag	Coverage Δ
unittests	81.15% <93.05%> (+0.82%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
btk/metrics.py	94.23% <87.50%> (+0.15%)	⬆️
btk/utils.py	90.69% <90.69%> (ø)
btk/__init__.py	100.00% <100.00%> (ø)
btk/draw_blends.py	85.58% <100.00%> (+0.58%)	⬆️
btk/measure.py	77.67% <100.00%> (+2.43%)	⬆️

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[thuiop]

This PR is ready to be reviewed ; the only shortcoming here is that PSF and WCS are not saved with the blends as galsim and astropy do not provide utility functions to do it cleanly. Should we use something like pickle to save it anyway ?

[ismael-mendoza]

Looks very good @thuiop, thanks for adding this functionality. Please see below for a couple of small requested changes and questions. It appears to me that it's really close to being ready for merge

[aboucaud]

I agree with @ismael-mendoza, one should be more attentive to how the save_path is constructed.

The way you wrote it, the user does not really have a choice for the filenames (probably a good thing), but it must have a choice of the main output directory then. If this is what you mean by save_path then we should use pathlib to construct the full paths.
Also it may be easier (we can discuss this) to create subdirectories inside the save_path to put the various outputs, e.g. save_path/survey/blended.npy rather than <save_path>_<survey>_blended.npy. That way it is easier to check the directory existence rather than the existence of each file before loading.

[thuiop]

I should have addressed all the comments.

[ismael-mendoza]

I think this is ready to merge after the CI passes and if my commit suggestions below are indeed what you intended.

[ismael-mendoza]

Thanks for resolving the merge conflicts @thuiop. Merging now -