Modernise OpenModelicaLibraryTesting

[AnHeuermann]

Issue

Updating or changing OpenModelicaLibraryTesting is an error prone and time consuming endeavor.

Some major issues:

• No versioned dependencies or suitable dependency management.
  • If a dependency changes in a breaking fashion we don't notice until it is too late.
  • OMPython 3.4.0 --> 4.0.0 introduced breaking changes. Only jobs that always re-install / update Python packages failed, while other which don't update didn't notice.
• No unit testing
  • Testing a whole library coverage is too slow for the CI.
• Dead code
  • There is unused code in the source files
  • Unused imports
• Monolithic code
  • Large functions or scripts are not separated into multiple smaller functions.
  • Very deep nesting of branching logic
• No documentation for sub-functions.
• No versioning

The Scripts are missing documentation and have a lot of dead code.
Testing of the scripts itself is slow and very rudimentary.

Suggested changes

• Transform scripts into Python package
  • Modern dependency management and build backend.
  • Directory layout with smaller sub-modules and one-file-per-function convention.
  • Unit tests with a modern testing framework.
  • Python docstrings
• Python documentation (MkDocs)

Suggested development process

• Develop on a new branch (Jenkins always uses latest master)
• Set aside a single Jenkins job to pick up the development version to assert it stays running as expected.
• Version the final OpenModelicaLibraryTesting module

[cbu-hw]

As part of this, maybe it's possible to make optional parts avoidable.
With https://github.com/OpenModelica/openmodelica-library-testing-action, this package is/should be useable for generic testing of Modelica packages. However, at the moment, using OMLT drags in a whole Julia installation, apparently for some Basemodelica-related checks that library authors I guess typically won't need.

In my case this Julia installation triggers some error which makes the Action (and I suspect a current version of OMLT, too) unusable for me (OpenModelica/openmodelica-library-testing-action#54), which would be avoidable if the Julia parts were Python optional-dependencies.