Improve performance of QuantumCircuit.append (#7134)
Improve performance of QuantumCircuit.append (#7134)

The method `set.issubset` takes a general iterable as an argument, and
only has special handling if the argument is strictly a `set`.  The `<=`
(subset) _operator_ on sets, however, permits anything which implements
the set ABC on the right, which means we no longer have to iterate
through something that is already set-like.  Dictionaries do not decay
implicitly to a set-like interface, but dictionary-view `keys` objects
do.

Co-authored-by: mergify[bot] <b09a6ee808b67e98a221404e7aaa52e0398a4954@users.noreply.github.com>
QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py