[Enhancement] Implement State Variables

[adtzlr]

Contique should be able to update the function args or at least some sub-elements containt state variables after each step. Therefore the equilibrium equation - function would have to return its args along the residuals.

[adtzlr]

Some ideas. This could be archieved by adding a

• callback function
• function returns updated state-variables beside the residuals

2nd option would be preferred.