* fix: `no_optional` should remove `Optional` * perf: improve vec creation * perf: remove temporary Vec * refactor: make dependency_groups testable * test: get_dependency_groups * refactor: remove unused imports * test: correct the specs * fix: get_dependency_groups * test: fix `should_install_dependencies` * feat: forbid unconsidered variant * test: add more to specs * feat: implement the remaining case * test: fix a test case * feat: --prod --dev should install optional * refactor: deref on init