Resolve "Add 'CantileverBeam' example"

Closes #85

See merge request mechanics-and-materials/ae108!74

- topological dimension no longer required
- add const

Resolve "Coverage badge does not show percentage"

Closes #109

See merge request mechanics-and-materials/ae108!98

Resolve "Memory leaks in `cpppetsc::Mesh`"

Closes #106

See merge request mechanics-and-materials/ae108!96

- fixes memory leaks

Resolve "Cobertura keyword no longer supported by GitLab"

Closes #107

See merge request mechanics-and-materials/ae108!97

- required by updated version of GitLab

- fixes error in CI

- provides vtkXdmfReader

- fixes error in CI

Resolve "Solve tests fail on Euler"

Closes #105

See merge request mechanics-and-materials/ae108!95

- fixes error in CI

- fixes test on Euler

- fixes error in CI

Resolve "Add support for lumped mass matrix computation"

Closes #103

See merge request mechanics-and-materials/ae108!93

- improves naming consistency

- real-valued even if value_type is complex (std::abs)

Resolve "Add support for consistent mass matrix computation"

Closes #102

See merge request mechanics-and-materials/ae108!92

Resolve "Job Failed #389789"

Closes #101

See merge request mechanics-and-materials/ae108!91

- fixes error in CI

- fixes error in CI

- fixes error in CI
- see https://github.com/psf/black/issues/2964