[AerUnitaryBackend] Call transpile() before run()

[cqc-alec]

Seems necessary to handle some gates that act on large numbers of qubits, such as C5X: see Qiskit/qiskit-aer#1855 .

[doug-q]

reproducer:

#!/usr/bin/env python3


from pytket.circuit import Circuit, CircBox, QControlBox
from pytket.extensions.qiskit import AerUnitaryBackend, AerStateBackend

backend = AerUnitaryBackend()
# backend = AerStateBackend() # using AerStateBackend does not raise an error

n_ancillas = 5 # using n_ancillas <=4 doees not raise an error
n_spins = 1
circ = Circuit(n_ancillas + n_spins)
trgt = Circuit(n_spins)
trgt.X(0)
# trgt.Y(0) # using Y instead of X does not raise an error

circ.add_qcontrolbox(
    QControlBox(CircBox(trgt), n_ancillas), list(range(n_ancillas + n_spins))
)

compiled_circ = backend.get_compiled_circuit(circ, optimisation_level = 0)
# using optimisation_level >= 1 does not raise an error
u = backend.run_circuit(compiled_circ)