Add stress test for 3d and combine in one function

[henrij22]

This is a small PR adding a stress test for linear 3D cube elements . We should discuss for a different PR how and if we want to modify this whole testing framework, maybe storing the expected values in the element formulation or sth like that.

For reference: my calulations come from these notebooks: https://github.tik.uni-stuttgart.de/HenrikJakob/elements-notebooks/tree/main

I might also add a test for 3d cube with EAS tommorow, so we can also add this to this PR

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (7e793d0) 89.81% compared to head (878870b) 91.55%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #208 +/- ## ========================================== + Coverage 89.81% 91.55% +1.73% ========================================== Files 44 42 -2 Lines 1904 1787 -117 ========================================== - Hits 1710 1636 -74 + Misses 194 151 -43 ``` | [Flag](https://app.codecov.io/gh/ikarus-project/ikarus/pull/208/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ikarus-project) | Coverage Δ | | |---|---|---| | [tests](https://app.codecov.io/gh/ikarus-project/ikarus/pull/208/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ikarus-project) | `91.55% <ø> (+1.73%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ikarus-project#carryforward-flags-in-the-pull-request-comment) to find out more.

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[henrij22]

I think that should work nicely. The good thing, is that we can then test everything (where we have nodal resutlts), not just stresses. I think for now i will stick to Eigen::Matrix to keep it simple, but in the feature we can also think about C++ 23 with its std::mdspan (here)

[henrij22]

@rath3t i think I have found a rather elegant way for the generalization. In the new file resultcollection.hh i created a lambda that gives the appropriate expectedResults, and then they are tested in the checkCalulateAt() Function

[henrij22]

If the CI is successfull, this should be ready from my side

[rath3t]

Thanks Henri. Nice addition!