Fix --nan-check false positive for finite/+INFINITY division

[tautschnig]

• Update NaN check condition to require infinity in nominator
• Add regression tests to validate IEEE 754 infinity arithmetic

Fixes: #8634

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• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
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[codecov]

Codecov Report

❌ Patch coverage is 52.00000% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.00%. Comparing base (1505c36) to head (5578125).

Files with missing lines	Patch %	Lines
src/solvers/smt2/smt2_parser.cpp	25.00%	12 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8745   +/-   ##
========================================
  Coverage    80.00%   80.00%           
========================================
  Files         1700     1700           
  Lines       188254   188273   +19     
  Branches        73       73           
========================================
+ Hits        150615   150631   +16     
- Misses       37639    37642    +3     

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