Added descriptive error text to assert statements

[cpilko]

Changes proposed in this pull request

• Added descriptive error text to two assert statements in interfaces/cython/cantera/composite.py

Closes #

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Checklist

• [ x ] The pull request includes a clear description of this code change
• [ x ] Commit messages have short titles and reference relevant issues
• [ ] Build passes (scons build & scons test) and unit tests address code coverage
• [ x ] Style & formatting of contributed code follows contributing guidelines
• [ x ] The pull request is ready for review

[bryanwweber]

Hi! Thanks for making this change. I think this is definitely an improvement.

Since you're editing these lines anyways, ideally we would actually change these into full if statements, raising an appropriate ValueError. The reason is that interpreter options can be set for Python that disable assert statements at runtime, so these guards would no longer be effective.

Please also address the changes suggested by the linter: https://github.com/Cantera/cantera/actions/runs/11936944028/job/33273168168?pr=1816, in particular making sure not to introduce any extra spaces at the ends of lines. You can continue to push changes to this branch to update the pull request.

Thank you!

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 20.00000% with 8 lines in your changes missing coverage. Please review.

Project coverage is 73.25%. Comparing base (ad41b31) to head (27312a5). Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
interfaces/cython/cantera/composite.py	20.00%	4 Missing and 4 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1816 +/- ## ========================================== - Coverage 73.26% 73.25% -0.02% ========================================== Files 383 383 Lines 54621 54625 +4 Branches 9099 9103 +4 ========================================== - Hits 40017 40013 -4 - Misses 11601 11605 +4 - Partials 3003 3007 +4 ```

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[bryanwweber]

Thank you! The test failures on macOS don't seem related to the changes here, but let's see what happens this time. I will merge this as soon as the tests look good!