Add tests for untested public Python API methods #2311

These public Python methods are not named in any test under python/*/tests. Found by checking each public method of the main API classes against the test sources. Getter methods (get_*, get*) are out of scope for this issue.

LP/MILP/QP modeling (cuopt/linear_programming/problem.py)

• Variable.setObjectiveCoefficient, Variable.setLowerBound, Variable.setUpperBound, Variable.setVariableName: the camelCase setters.
• LinearExpression.zipVarCoefficients
• Problem.Obj

DataModel (cuopt/linear_programming/data_model/data_model.py)

• clear_quadratic_constraints
• set_variable_names, set_row_names, set_objective_name, set_problem_name: set, then check they are kept (for example through an MPS write and read back).

Solution (cuopt/linear_programming/solution/solution.py)

• raise_if_lp_solution, raise_if_milp_solution: check each raises for the wrong problem type and does not for the right one.

Routing

• re_routing.generate_capacity_constraints_for_vehicle_order_match
• Assignment.display_routes

Docs

• python/cuopt/cuopt/tests/routing/API_COVERAGE.md says display_routes() is covered by test_vehicle_properties and the Assignment getters by test_solver. display_routes is not named in any test, so the table is stale. Update it once the tests are in.

Out of scope here

The cuopt_sh command-line options --upload-solution, --cache, --delete, --only-validation, --warmstart-id, --queued, --running and --status also have no direct test. Track them separately if wanted.