Zerod connector nodes

[ischoegl]

Changes proposed in this pull request

This PR pulls out the less controversial modifications from #1788, while improving the nomenclature (see Cantera/enhancements#213 (comment)):

• Create a new ConnectorNode base, which combine Wall and FlowDevice objects; all objects are captured in updated factories.
• Changes are propagated to all relevant API’s, i.e. Python, CLib and MATLAB.

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

Addresses Cantera/enhancements#213

Checklist

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

[codecov]

Codecov Report

Attention: Patch coverage is 57.57576% with 70 lines in your changes missing coverage. Please review.

Project coverage is 74.34%. Comparing base (e6f3e9d) to head (3822451).

Files with missing lines	Patch %	Lines
src/clib/ctreactor.cpp	13.95%	37 Missing ⚠️
src/zeroD/ConnectorFactory.cpp	58.82%	14 Missing ⚠️
interfaces/cython/cantera/reactor.pyx	80.00%	6 Missing ⚠️
src/zeroD/FlowDevice.cpp	86.36%	3 Missing ⚠️
src/zeroD/Wall.cpp	66.66%	3 Missing ⚠️
include/cantera/zeroD/ConnectorNode.h	80.00%	2 Missing ⚠️
src/zeroD/ReactorBase.cpp	66.66%	2 Missing ⚠️
include/cantera/zeroD/FlowDevice.h	0.00%	1 Missing ⚠️
include/cantera/zeroD/Wall.h	0.00%	1 Missing ⚠️
src/zeroD/ConnectorNode.cpp	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1848      +/-   ##
==========================================
- Coverage   74.41%   74.34%   -0.07%     
==========================================
  Files         386      387       +1     
  Lines       53628    53623       -5     
  Branches     9063     9066       +3     
==========================================
- Hits        39905    39867      -38     
- Misses      10652    10689      +37     
+ Partials     3071     3067       -4     

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