Fix classical control rendering for gate

[gadhvirushiraj]

• Fixed rendering issue for classical control on gates for both renderers.
• Optimize: Removed _draw_singleq_gate for rendering in MatRenderer.

[BoxiLi]

Thanks a lot for such a quick PR!

I noticed two things:

1. This classical control line should also be added when we compute the layer of the gate.

from qutip_qip.circuit import QubitCircuit
qc = QubitCircuit(2, num_cbits=2)
qc.add_gate("X", targets=0, classical_controls=0, classical_control_value=0)
qc.add_gate("X", targets=1, classical_controls=1, classical_control_value=1)
qc.draw()

2. I think there might be a misunderstanding of the classical_controls and classical_control_value. I didn't realize it when you asked that question on Discord. I think here we should read classical_controls, which should be a list that records the control classical bits. And then we draw a circuit on it, like in the quantum controlled gate

[gadhvirushiraj]

1. This classical control line should also be added when we compute the layer of the gate.

We dont maintain a record for classical lines. But we just augment this by maintaining gaps in qlines. But it should be now fixed for MatRenderer.

I have modified it to read classical_controls too.

Edit: TextRenderer is yet to fix

[BoxiLi]

Great! Looks good!

[BoxiLi]

Looks good! Rendered nicely on my machine. Would be nice to add one test case for the text renderer. Just to be safe.

The failing test is unrelated, but the one on matplotlib seems to be a warning from the old matplotlib 3.9

[BoxiLi]

Thanks! This looks good to me. Shall I merge? @gadhvirushiraj