Run full model code generation for test models during CI from Python

[dweindl]

Currently model code is pregenerated from Matlab, due to Matlab not being available on CI servers. We should implement those models so that they are importable from Python. (Some features still missing). This will test the import functionality and performance more regularly.

[paulstapor]

We could create test jobs such as for the SBML test suite, which are at least run if a new PR for master is to be merged. It doesn't need to be tested for every little PR. There's also no need for highly complex models, but a little set of maybe 3-5ish models with different features, maybe some with even analytical solutions, would already back many things we're doing...