Use the rounded new_R values in change_unit_cell.

Previously, the `new_R` values were checked to be close to an
integer, but then the conversion to `int` happened directly via
`astype(int)` instead of using the rounded values.

This could lead to incorrect results - but it is not expected to
have been common, because the new unit cell in reduced coordinates
is an integer matrix.

Author: greschd

tbmodels/_tb_model.py

@@ -1635,7 +1635,7 @@ def change_unit_cell(  # pylint: disable=too-many-branches
         for R, hop_mat in self.hop.items():
             new_R = la.solve(uc_reduced.T, R)
             assert np.allclose(np.round(new_R), new_R)
-            new_R = tuple(new_R.astype(int))
+            new_R = tuple(np.round(new_R).astype(int))
             new_hop[new_R] = hop_mat
 
         return Model(