MultiIndexSet make_complete does not complete

The make_complete function of MultiIndexSet is missing certain exponents which should appear after completion. Ideally, it should be based on the lp_degree.

A minimal code to reproduce the issue:

import numpy as np
from minterpy import MultiIndexSet

mi = MultiIndexSet(np.array([[0, 0],
                             [2, 0],
                             [0, 2]]))

mi_completed = mi.make_complete()

mi2 = MultiIndexSet.from_degree(spatial_dimension=2,
                                poly_degree=2,
                                lp_degree=2.0)

assert mi2 == mi_completed