No wireswap handling in the creation of a phase poly box

[cqc-melf]

Wireswaps are not handled in the creation of a phase poly box, this should be changed.

Circuit circ(2);
circ.add_op<unsigned>(OpType::SWAP, {0, 1});
circ.replace_SWAPs();
std::cout << "has wireswaps: " << circ.has_implicit_wireswaps()
          << std::endl;
PhasePolyBox ppbox(circ);
std::shared_ptr<Circuit> circptr = ppbox.to_circuit();
Circuit circ2 = *circptr;
for (auto c : circ2) {
  c.print();
}
std::cout << "has wireswaps: " << circ2.has_implicit_wireswaps()
          << std::endl;
REQUIRE(test_unitary_comparison(circ, circ2));

Will fail with:

Begin testcase: single SWAP circuit in PhasePolyBox
has wireswaps: 1
has wireswaps: 0

test_tket is a Catch v2.13.7 host application.
Run with -? for options

FAILED:
  REQUIRE( test_unitary_comparison(circ, circ2) )
with expansion:
  false