Mark `clib` as experimental

[ischoegl]

Changes proposed in this pull request

After the removal of the legacy MATLAB toolbox in #1670, all remaining interfaces that use clib are either experimental (matlab_experimental) or rudimentary/incomplete (Fortran, .NET).

The proposed change allows for a faster development cycle to fix accumulated issues and inconsistencies until stable APIs have been implemented.

There are actually no code changes, which may be pursued in other PRs.

If applicable, fill in the issue number this pull request is fixing

Resolves Cantera/enhancements#211

Checklist

• [x] The pull request includes a clear description of this code change
• [x] Commit messages have short titles and reference relevant issues
• [x] 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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 73.20%. Comparing base (fdefc11) to head (9e6d7d8).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1769 +/- ## ======================================= Coverage 73.19% 73.20% ======================================= Files 381 381 Lines 54289 54289 Branches 9242 9242 ======================================= + Hits 39737 39740 +3 + Misses 11579 11577 -2 + Partials 2973 2972 -1 ```

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