A simple solver for small strain problems

[srosenbu]

Although, we don't want to make this a comprehensive library, at least for the standard incremental small strain models, we should have a solver/or problem definition similar to dolfinx.fem.petsc.NonlinearProblem

[pdiercks]

the ramberg osgood plasticity model belongs to that class of models. Therefore, we could address this issue and #34 with a single PR. sounds good?

[srosenbu]

Sounds good;) Do you plan on doing the model with numba or is it possible to use numpy functions for everything?

[pdiercks]

It would be simplest to use the old implementation using numba or implement the same function with cpp or rust if we dont want to use numba.

[srosenbu]

I don't see a problem with using numba