Update circuit helper methods to handle list of size one

[jplewa]

Summary

Updates the qiskit_to_ionq and qiskit_circ_to_ionq_circ helper methods to support a single element, or a list of size one, when being invoked.

Details and comments

This is in accordance with the changes introduced in #71. Support for multi-circuit experiments should probably be added to these methods when #70 is addressed.

[jplewa]

Upon further consideration, I'm not sure if these changes are necessary. The issues that I described in #70 and microsoft/azure-quantum-python#200 do play out in the form of qiskit_circ_to_ionq_circ errors, but I think it's just because IonQBackend in azure-quantum doesn't handle circuit lists properly. The proper fix would be to update IonQBackend instead. These helper methods are probably fine the way they are now, unless anyone finds the changes useful in any way ;)