feat: Split program sets

[speller26]

Introduce split method to ProgramSet to split program set into a list of program sets each with at most an allowed number of executables.

Also fixed coverage output when running tox.

Issue #, if available:

Description of changes:

Testing done:

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (11065d0) to head (da10d72).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1249   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          169       169           
  Lines        10963     11061   +98     
  Branches      1412      1433   +21     
=========================================
+ Hits         10963     11061   +98     

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[sesmart]

Very cool 😄, just some notes on usability. Any reason the input_set is taken as the major counting index before observables? Just coincidence of orderings?

[speller26]

Results merging has been moved to #1254