Resolve "ForceElement example fails when using MPI"

Closes #100

See merge request mechanics-and-materials/ae108!89

- fixes mypy error in CI

- output test requires "--planar" flag
- fixes error in CI

- permits selection of preference in case of ambiguity

- fixes pylint error in CI

- corrects XDMF for CuboidMesh example

- permits mixed numbers of vertices
- guess quadrilateral/tetrahedron based on coordinate dimension

Resolve "Check example HDF5 output in CI"

Closes #64

See merge request mechanics-and-materials/ae108!90

- fixes error in CI

- complex-valued output can now be compared with real-valued references
- fixes error in CI

- see #100

- sorting may not work as expected
- e.g. for small changes in first coordinate

- fixes error in CI

- compares binary output by converting to VTU first

- vtu files contain data as ASCII, which simplifies comparisons in tests

- compares properties of unstructured grids

- add __init__.py

- required by vtk library
- fixes error in CI

- install vtk via pip

- simplifies comparisons (ASCII)

Resolve "IsGroupTypeTrait not found if plugin in different namespace"

Closes #99

See merge request mechanics-and-materials/ae108!88

- add test in ae108::assembly namespace
- add test in other namespace (#99)

- required for plugins that are not in the ae108::assembly namespace

- KSP converges without preconditioner with FGMRES

- ubuntu jammy provides 0.11.0
- fixes error in CI

- PETSc now prints information about celltype label