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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[codecov]

Codecov Report

❌ Patch coverage is 84.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.00%. Comparing base (bacf91c) to head (5702d00).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/solvers/smt2/smt2_parser.cpp	75.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8745      +/-   ##
===========================================
- Coverage    80.01%   80.00%   -0.01%     
===========================================
  Files         1700     1700              
  Lines       188344   188364      +20     
  Branches        73       73              
===========================================
+ Hits        150701   150710       +9     
- Misses       37643    37654      +11     

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[Copilot]

Pull request overview

Fixes a --nan-check false positive by aligning division NaN detection with IEEE 754 rules (finite/∞ is ±0, only ∞/∞ yields NaN), and adds regressions around infinity arithmetic.

Changes:

• Update NaN-check logic for division to flag only 0/0 and inf/inf.
• Extend SMT2 parser support with fp.isNegative / fp.isPositive.
• Add/adjust regression tests and math-library stubs for __isfinite*.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/util/ieee_float.cpp	Updates division comment to reflect IEEE 754 behavior.
src/solvers/smt2/smt2_parser.cpp	Adds parsing for fp.isNegative and fp.isPositive.
src/ansi-c/library_check.sh	Excludes __isfinite* symbols from library check list.
src/ansi-c/library/math.c	Adds __isfinite, __isfinitef, __isfinitel wrappers.
src/ansi-c/goto-conversion/goto_check_c.cpp	Fixes NaN check condition for division (inf/inf only).
src/ansi-c/c_typecheck_expr.cpp	Treats __builtin_isfinite as a special function.
regression/cbmc/float-nan-check/test.desc	Updates expected NaN-check failure pattern for division.
regression/cbmc/float-nan-check/main.c	Adjusts regression to use inf/inf instead of n/inf.
regression/cbmc/float-inf-div-inf/test.desc	Adds new regression expectations for inf/inf NaN checks.
regression/cbmc/float-inf-div-inf/main.c	New test exercising ±inf / ±inf producing NaN.
regression/cbmc/float-finite-div-infinity/test.desc	New regression ensuring finite/∞ does not trigger NaN checks.
regression/cbmc/float-finite-div-infinity/main.c	New test asserting finite/∞ results in signed zero.

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