Allow passing in and returning the quantum register when loading cirq.Circuits into squin

[david-pl]

While looking into this I realized that the only thing that makes sense (IMO) to pass into or return from a circuit is the list of qubits. I added two simple keyword arguments to control the behavior.

The result is that you can compose kernels that you can easily compose kernels that you generate from circuits. For example:

q = cirq.LineQubit.range(2)
circuit = cirq.Circuit(cirq.H(q[0]), cirq.CX(*q))

get_entangled_qubits = squin.cirq.load_circuit(
    circuit, return_register=True, kernel_name="get_entangled_qubits"
)
get_entangled_qubits.print()

entangle_qubits = squin.cirq.load_circuit(
    circuit, register_as_argument=True, kernel_name="entangle_qubits"
)

@squin.kernel
def main():
    qreg = get_entangled_qubits()
    qreg2 = squin.qubit.new(1)
    entangle_qubits([qreg[1], qreg2[0]])
    return squin.qubit.measure(qreg2)

Here, get_entangled_qubits allocates a new register, entangles it and returns the result, whereas entangle_qubits accepts a register of two qubits to entangle. Of course, you could also pass in and return from the same kernel by setting both return_register=True and register_as_argument=True.

FYI, @jon-wurtz , let me know if this covers the use case you had in mind.

Closes #302

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☂️ Python Coverage

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Lines	Covered	Coverage	Threshold	Status
8806	7769	88%	0%	🟢

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Modified Files

File	Coverage	Status
src/bloqade/squin/cirq/_init_.py	94%	🟢
src/bloqade/squin/cirq/lowering.py	93%	🟢
TOTAL	94%	🟢

updated for commit: 1349feb by action🐍