Introducing BinPairSelector class system for bin pair selection.

[vitenti]

Description

This PR introduces a framework for bin pair selection in two-point correlation functions through a hierarchy of BinPairSelector classes. The design allows users to define, combine, and reuse rules for filtering InferredGalaxyZDist bins and their measurements before constructing TwoPointXY objects. This addresses the need to systematically and safely generate physically meaningful combinations, beyond simple “all compatible pairs”. The tutorials were reorganized to include this new feature and a new tutorial document detailing BinPairSelector was added.

Type of change

Please delete the bullet items below that do not apply to this pull request.

• New feature (non-breaking change which adds functionality)

Checklist:

The following checklist will make sure that you are following the code style and
guidelines of the project as described in the
contributing page.

• I have run bash pre-commit-check and fixed any issues
• I have added tests that prove my fix is effective or that my feature works
• I have made corresponding changes to the documentation
• I have 100% test coverage for my changes (please check this after the CI system has verified the coverage)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.0%. Comparing base (855ac88) to head (9e76bd2).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master     #552    +/-   ##
========================================
  Coverage   100.0%   100.0%            
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  Files         150      151     +1     
  Lines        8787     9035   +248     
  Branches     1012     1033    +21     
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+ Hits         8787     9035   +248     

Files with missing lines	Coverage Δ
firecrown/generators/_inferred_galaxy_zdist.py	100.0% <ø> (ø)
firecrown/metadata_functions/__init__.py	100.0% <ø> (ø)
firecrown/metadata_functions/_combination_utils.py	100.0% <100.0%> (ø)
firecrown/metadata_functions/_extraction.py	100.0% <100.0%> (ø)
firecrown/metadata_types/__init__.py	100.0% <100.0%> (ø)
firecrown/metadata_types/_inferred_galaxy_zdist.py	100.0% <100.0%> (ø)
firecrown/metadata_types/_measurements.py	100.0% <100.0%> (ø)
firecrown/metadata_types/_pair_selector.py	100.0% <100.0%> (ø)
firecrown/metadata_types/_sacc_type_string.py	100.0% <100.0%> (ø)
firecrown/metadata_types/_utils.py	100.0% <100.0%> (ø)

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