Support Sundials 6.0 and 6.1

[bryanwweber]

CVodeGetNumStepSolveFails is only defined in SUNDIALS 6.2 and up. Since the previous version check had a typo, this code was never included.

Closes #1771

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.19%. Comparing base (5393a88) to head (b97af88).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1774      +/-   ##
==========================================
- Coverage   73.20%   73.19%   -0.01%     
==========================================
  Files         381      381              
  Lines       54289    54289              
  Branches     9242     9242              
==========================================
- Hits        39740    39737       -3     
- Misses      11577    11579       +2     
- Partials     2972     2973       +1     

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