Implement `qk_circuit_from_python`

[garrison]

#14314 introduced a qk_circuit_to_python function, but it is currently not possible to do the reverse operation. (In other words, once a circuit becomes a python circuit, it must always then be a python circuit.) Is there anything preventing a corresponding qk_circuit_from_python function from existing? If not, it would be nice to have it.

[mtreinish]

The python circuit can contain objects that we have no representation of in the C API and it also breaks the assumptions made in the transpiler around the circuits they can encounter.

The most concrete example of this is if you built a parameterized circuit in Python and then ran qk_circuit_to_python nothing in the C API for circuits as it exists right now is able to deal with the parameters. Like if you did qk_circuit_get_instruction() it would panic and crash the program.

[mtreinish]

It's probably worth pointing out that I did a version of this for: #14958 but it's not exactly what I think you're asking for here. It's not moving ownership from Python to C without a copy, it is basically iterating over the Python circuit to build a copy of the circuit using the C API. It's also obviously not a general solution it only works for a subset of circuits and right now it doesn't even support everything in the C API, just enough to test what we need to. We're not likely to add anything like this to the public API but it's fairly easy to build using ctypes if that is useful for your use case.

[jakelishman]

This was done in #15767