Apply channel for Clifford circuits with cupy

[AlejandroSopena]

This PR fixes a TypeError when using noise channels in Clifford circuits and running them with the CliffordBackend on GPU. It can be reproduced with the following code extracted from test_backends_clifford.py:

import numpy as np
from qibo import gates
from qibo.backends import CliffordBackend
from qibo.quantum_info import random_clifford
from qibo.noise import NoiseModel, PauliError

backend = CliffordBackend('cupy')

nqubits = 3

c = random_clifford(nqubits, density_matrix=True, backend=backend)

noise = NoiseModel()
noisy_gates = np.random.choice(c.queue, size=1, replace=False)
noise.add(PauliError([("X", 0.3)]), noisy_gates[0].__class__)

c.add(gates.M(*range(nqubits)))

c = noise.apply(c)

result = backend.execute_circuit(c)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.99%. Comparing base (d8cc501) to head (3f471a7).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1404   +/-   ##
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  Coverage   99.99%   99.99%           
=======================================
  Files          78       78           
  Lines       11192    11193    +1     
=======================================
+ Hits        11191    11192    +1     
  Misses          1        1           

Flag	Coverage Δ
unittests	99.99% <100.00%> (ø)

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