Finish rewrite of user cuts component

tests/components/test_objective.py

@@ -7,9 +7,12 @@ from unittest.mock import Mock
 import pytest
 from numpy.testing import assert_array_equal
 
-from miplearn import GurobiPyomoSolver, LearningSolver, Regressor, Instance
+from miplearn.classifiers import Regressor
 from miplearn.components.objective import ObjectiveValueComponent
 from miplearn.features import TrainingSample, InstanceFeatures, Features
+from miplearn.instance import Instance
+from miplearn.solvers.learning import LearningSolver
+from miplearn.solvers.pyomo.gurobi import GurobiPyomoSolver
 from tests.fixtures.knapsack import get_knapsack_instance
 
 import numpy as np