DevContainer: add real and complex container, fix permission issues

See merge request mechanics-and-materials/ae108!149

- Remove adding in CI run (added to docker image now)
- Install llvm 18 in order to have up to date clang-tidy

containers were running with root user which caused in issues when creating files

Examples

See merge request mechanics-and-materials/ae108!146

docs: Migrate from sphinx to mkdocs

See merge request mechanics-and-materials/ae108!143

Meshing

See merge request mechanics-and-materials/ae108!142

Update docker-compose.yml

See merge request mechanics-and-materials/ae108!141

Resolve "Use aggregate initialization instead of constructors"

Closes #119

See merge request mechanics-and-materials/ae108!108

Start using C++20

See merge request mechanics-and-materials/ae108!140