Add const terms for nodes, utils and NL OPt

src/classification/ConvexHull1D.cpp

src/classification/ConvexHull1D.hpp

src/descriptor_identifier/Model/Model.hpp

src/descriptor_identifier/Model/ModelClassifier.cpp

src/descriptor_identifier/Model/ModelRegressor.cpp

src/descriptor_identifier/SISSO_DI/SISSOClassifier.cpp

src/descriptor_identifier/SISSO_DI/SISSOLogRegressor.cpp

src/descriptor_identifier/SISSO_DI/SISSORegressor.cpp

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.cpp

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

...lowed_operator_nodes/abs/parameterized_absolute_value.cpp