num_duplicate_paulis cannot distinguish from num_trimmed_paulis

[caleb-johnson]

The reported values extracted in the qiskit_addon_obp.utils.simplify module cannot distinguish the difference between duplicate and trimmed paulis (e.g. due the tolerance).

[mrossinek]

Just some additional info here:

• there is already a unittest which should cover this prepared here (it just has to be uncommented once fixed):

  qiskit-addon-obp/test/utils/test_simplify.py

  Lines 110 to 113 in bdd9509

  	# FIXME: the following fails due to a known bug. The `num_duplicate_paulis` cannot
  	# differentiate between actual duplicates and values which have been trimmed due to the
  	# chosen tolerances.
  	# self.assertEqual(metadata.num_duplicate_paulis, 0)

• a fix for this will have to update the following logic which will already disregard close-to-zero values from the entire simplification process:

  qiskit-addon-obp/qiskit_addon_obp/utils/simplify.py

  Lines 122 to 125 in bdd9509

  	non_zero = np.logical_not(np.isclose(operator.coeffs, 0, atol=atol, rtol=rtol))
  	paulis_x = operator.paulis.x[non_zero]
  	paulis_z = operator.paulis.z[non_zero]
  	nz_coeffs = operator.coeffs[non_zero]