Create SPECT subsets from ProjData

[samdporter]

Changes in this pull request

Add ability to create SPECT subsets with partitioner (as separate ProjData)

Testing performed

None, as yet. Tests require template data (I'll sort this soon)

Related issues

Fixes segfaults arising from using partitioner (SIRF-contribs) on SPECT ProjData

Checklist before requesting a review

• [] I have performed a self-review of my code
• [] I have added docstrings/doxygen in line with the guidance in the developer guide
• I have implemented unit tests that cover any new or modified functionality (if applicable)
• The code builds and runs on my machine
• [] documentation/release_XXX.md has been updated with any functionality change (if applicable)

[KrisThielemans]

3 small changes required.

Also, how different is src/test/test_proj_data_info_subsets_spect.cxx from PET? I didn't check, but it's likely most of it is the same. Easy to avoid overlap? (could derive both from one class)

[samdporter]

Hmm... this worked on my local machine - segfaults here.

[KrisThielemans]

The Debug build has the following: https://github.com/UCL/STIR/actions/runs/18319764443/job/52169585055?pr=1596#step:12:231

	Setting up projector pair with ProjMatrixByBinSPECTUB
	Testing Subset forward projection is consistent with reduced segment range
Initial segment range: min_segment_num = 0, max_segment_num = 0
test_proj_data_info_subsets_spect: /home/runner/work/STIR/STIR/src/buildblock/ProjDataInfo.cxx:337: virtual void stir::ProjDataInfo::reduce_segment_range(int, int): Assertion `min_segment_num >= get_min_segment_num()' failed.

[KrisThielemans]

Also, how different is src/test/test_proj_data_info_subsets_spect.cxx from PET? I didn't check, but it's likely most of it is the same. Easy to avoid overlap? (could derive both from one class)

I did check. There is some scope for reducing overlap, e.g. by putting the code that explicitly loops over viewgrams to check if they are the same in both PET and SPECT versions etc. However, this will have to remain for later.

[KrisThielemans]

I've done some minor clean-up. If (when?) tests succeed, I'll squash-merge this. Let me know ASAP if you prefer a normal merge.