Further coverage updates

.gitlab-ci.yml

src/CMakeLists.txt

src/descriptor_identifier/model/Model.cpp

src/descriptor_identifier/model/ModelRegressor.hpp

src/feature_creation/feature_space/FeatureSpace.cpp

src/feature_creation/feature_space/FeatureSpace.hpp

src/feature_creation/node/FeatureNode.cpp

src/feature_creation/node/FeatureNode.hpp

src/feature_creation/node/ModelNode.cpp

src/feature_creation/node/ModelNode.hpp

src/feature_creation/node/Node.cpp

src/feature_creation/node/Node.hpp

src/feature_creation/node/operator_nodes/OperatorNode.hpp

...rator_nodes/allowed_operator_nodes/abs/absolute_value.hpp

...lowed_operator_nodes/abs/parameterized_absolute_value.hpp

...s/allowed_operator_nodes/abs_diff/absolute_difference.hpp

...ator_nodes/abs_diff/parameterized_absolute_difference.hpp

...on/node/operator_nodes/allowed_operator_nodes/add/add.hpp

...or_nodes/allowed_operator_nodes/add/parameterized_add.hpp

...on/node/operator_nodes/allowed_operator_nodes/cb/cube.hpp