kaldag

> Thanks for this Kalyan. We should also add a test that the warning is raised, both for directly adding qubits, for adding them implicitly via `add_register(QuantumRegister)`, and also that...

> Thanks Kalyan - this looks sensible, the review's just minor wording stuff then it's mergeable. Thanks a lot for the review @jakelishman. I have made all the changes you...

Thanks Jake for the review. I have added all the tests you suggested. Also added `input_qubit_mapping`.

Yen's algorithm was used to get the k-shortest path. This builds on top of an existing shortest path algorithm, like the Dijkstra's algorithm, etc. More on Yen's algorithm - https://people.csail.mit.edu/minilek/yen_kth_shortest.pdf