Linear regularisation demos

[emorice]

While trying to create a test case for non-linearity handling, we accidentally created a case to demonstrate instabilities in high-dimensional linear models. The fact it happened easily and comparison to real data in terms of spectra suggests this is a generic problem that needs to be handled by any candidate model, and thus a valuable test case to have in itself.

• [x] Factor out linear and kmeans in models (negative control)
• [x] Refactor current accidental case into a lin reg case
• [x] add a positive control (e.g. cv-based ridge or pca)
• [x] add cmk
• [x] add ~wmk~ something wishart-based

[emorice]

For wmk: tried something of that sort already, it seems off

[emorice]

Cmk integrated as of be27471abe41e461c91bd933572c96a17a257f9b