Make Float Integer comparisons more robust

[kwabenantim]

Description

Make singularity checks robust to Float/Integer equality using is_zero.

Motivation and Context

Supports #376

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Documentation checklist

• I have updated all documentation in the code where necessary.
• I have checked spelling in all (new) comments and documentation.
• I have added a note to RELEASE.md if relevant (new feature, breaking change, or notable bug fix).

Testing

• Testing is done automatically and codecov shows test coverage
• This cannot be tested automatically

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (c09e4aa) to head (0ae700e).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #385   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines         1594      1594           
  Branches       328       328           
=========================================
  Hits          1594      1594           

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[Copilot]

Pull request overview

This PR updates singularity detection/fixing logic to use SymPy’s .is_zero semantics instead of direct numeric comparisons, making zero-checks behave consistently across Float vs Integer representations (supporting SymPy 1.13–1.14 per #376).

Changes:

• Replaced != 0 coefficient checks with not <expr>.is_zero in singularity pattern matching.
• Made reciprocal detection (1/A) robust by detecting exponent -1 via (exp + 1).is_zero rather than float(exp) == -1.0.

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