Changes proposed in this pull request

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• Eliminate size_t from CLib API
• Use const double* consistently for all setters
• Eliminate SharedCabinet::item and SharedCabinet::get
• Eliminate magic numbers from thermo_equilibrate
• Eliminate various legacy constructors

Currently missing: ensure safe casting of size_t to int, ...

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

Closes #1450
Partially addresses Cantera/enhancements#199 (.NET side)

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

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