300 add a poisson solver case to the profiling examples

[spossann]

Solves the following issue(s):

Closes #300

[max-models]

When you agree, then I'll merge this branch @spossann

[max-models]

Here is an example of the strong scaling test: https://struphy-hub.github.io/profiling-data/figures/?case=20260730T094119Z-5e4d2dda-poisson_cube_strong_scaling#cases

Clearly we should increase the size of the problem, but I think we can do that in a separate PR after we merged this one and #301

[spossann]

I will now add some post-processing to the test case, to be sure that the result is correct.

[max-models]

Do you want to add a postprocessing and verification step to this PR before merging? @spossann

[spossann]

Do you want to add a postprocessing and verification step to this PR before merging? @spossann

Ok, we can do it in a separate PR, let's merge. I have colloquium now, will be absent unitl 13h00.

[max-models]

Do you want to add a postprocessing and verification step to this PR before merging? @spossann

Ok, we can do it in a separate PR, let's merge. I have colloquium now, will be absent unitl 13h00.

Ok!