Make is-zero-checks compatible with the upcoming sympy>1.12

[dweindl]

Current sympy master (tested: 0ededfcfc033ddca2d1d54a0eda85bf53c63761c):

IPython console for SymPy 1.13.dev (Python 3.12.2-64-bit) (ground types: python)
In [1]: Float(0) == 0
Out[1]: False
In [2]: Float(0).is_zero
Out[2]: True

vs 1.12:

Python console for SymPy 1.12 (Python 3.12.2-64-bit) (ground types: python)
>>> Float(0) == 0
True
>>> Float(0).is_zero
True

Therefore, replace == 0 by .is_zero.

Amongst other potential issues, this fixes zeros in sparse matrices. Closes #2320.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.94%. Comparing base (2235ab7) to head (d3e069e).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2350      +/-   ##
===========================================
+ Coverage    77.86%   77.94%   +0.07%     
===========================================
  Files          324      324              
  Lines        20731    20731              
  Branches      1449     1449              
===========================================
+ Hits         16143    16159      +16     
+ Misses        4585     4569      -16     
  Partials         3        3              

Flag	Coverage Δ
cpp	73.74% <100.00%> (+0.07%)	⬆️
cpp_python	34.34% <100.00%> (ø)
petab	36.86% <66.66%> (ø)
python	72.52% <100.00%> (+0.07%)	⬆️
sbmlsuite	?

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Files	Coverage Δ
python/sdist/amici/cxxcodeprinter.py	90.19% <100.00%> (ø)
python/sdist/amici/de_model.py	92.63% <100.00%> (ø)

... and 4 files with indirect coverage changes