Fix load bug for large models

[sebapersson]

Before all reactions were collected in a vector. For models with more than 58,000 reactions this caused stackoverflow, now reactions are added one at a time with addreaction!.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.38%. Comparing base (9a4cd00) to head (7f16e44).
Report is 117 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
- Coverage   95.39%   95.38%   -0.01%     
==========================================
  Files          16       16              
  Lines        1759     1778      +19     
==========================================
+ Hits         1678     1696      +18     
- Misses         81       82       +1     

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