Use Solution for zeroD objects

[ischoegl]

Changes proposed in this pull request

• Assign Solution to zeroD objects where possible
• Implement instantiation of non-empty Reactor objects, and trigger deprecation warnings when attempting to create reactors without content whenever feasible
• Some legacy routes for empty Reactor objects remain (example: legacy MATLAB toolbox)

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

Prepares a future solution for #1457

If applicable, provide an example illustrating new features this pull request is introducing

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

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (8d676c0) 72.78% compared to head (62300d3) 72.77%. Report is 5 commits behind head on main.

:exclamation: Current head 62300d3 differs from pull request most recent head f653e69. Consider uploading reports for the commit f653e69 to get more accurate results

Files	Patch %	Lines
src/zeroD/ReactorBase.cpp	66.66%	4 Missing and 1 partial :warning:
src/clib/ctreactor.cpp	50.00%	3 Missing :warning:
src/zeroD/ReactorFactory.cpp	71.42%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1663 +/- ## ========================================== - Coverage 72.78% 72.77% -0.01% ========================================== Files 375 375 Lines 56610 56629 +19 Branches 20510 20521 +11 ========================================== + Hits 41201 41212 +11 - Misses 12389 12395 +6 - Partials 3020 3022 +2 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[ischoegl]

@speth ... thanks for the review! As there aren't unit tests for that portion available yet, I tested the modifications of the "experimental" MATLAB toolbox locally (with the side-effect that I now have MATLAB for Apple Silicon installed). So I guess this should be ready ...