SBML import: avoid repeated xdot==0 checks

[dweindl]

Avoid checking for xdot==0 for every single event when computing deltasx.

Avoid avoid some extra matrix multiplication, which may result in undefined symbols for some funny models where xdot==0.

Update SBML test suite triggers.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.91%. Comparing base (9ea6aef) to head (5147aa6).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2706   +/-   ##
========================================
  Coverage    77.91%   77.91%           
========================================
  Files          326      326           
  Lines        23004    23006    +2     
  Branches      1479     1479           
========================================
+ Hits         17924    17926    +2     
  Misses        5069     5069           
  Partials        11       11           

Flag	Coverage Δ
cpp	74.76% <100.00%> (+<0.01%)	⬆️
cpp_python	33.59% <100.00%> (+0.01%)	⬆️
petab	39.41% <25.00%> (-0.02%)	⬇️
python	72.96% <100.00%> (+<0.01%)	⬆️

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Files with missing lines	Coverage Δ
python/sdist/amici/de_model.py	90.35% <100.00%> (+0.02%)	⬆️

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