Support .sbml model file extension

[rachybio]

Summary

I tested issue #131 against the current MICOM release (v0.39.1) and confirmed that .sbml files were still not supported by micom.util.load_model().

Attempting to load a .sbml model resulted in:

KeyError: '.sbml'

This PR adds support for the .sbml extension and includes a regression test to ensure it can be loaded correctly.

Changes

• Added .sbml to MICOM's model reader mapping.
• Added a regression test for .sbml model loading.

Testing

• Reproduced the issue on MICOM v0.39.1 before the fix.
• pytest tests/test_util.py::test_load_sbml_extension -q
• pytest tests/test_util.py -q

Both tests pass after the fix.

Closes #131

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.37%. Comparing base (3bff1ca) to head (81f27ad).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #249   +/-   ##
=======================================
  Coverage   81.37%   81.37%           
=======================================
  Files          39       39           
  Lines        2303     2303           
  Branches      318      318           
=======================================
  Hits         1874     1874           
  Misses        294      294           
  Partials      135      135           

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[cdiener]

Thanks!