Set num_qubits kwarg when building UnitaryGate from Rust (#13282)

In the accelerate crate we currently have two places that are building
`UnitaryGate`, the quantum_volume() function that builds a quantum
volume model circuit and the Split2QUnitaries transpiler pass. Currently
this can only be done by calling Python (until #13272 is implemented)
and there was a potential optimization we could make to specify the
number of qubits as an argument to the Python constructor. This skipss
the need for a few python operations to compute the number of qubits
from the size of the matrix. These operations are not exceedingly slow,
but as these Python space constructors are often the bottleneck so it
should help runtime performance of these two functions.

crates/accelerate/src/circuit_library/quantum_volume.rs

@@ -10,7 +10,9 @@
 // copyright notice, and modified files need to carry a notice indicating
 // that they have been altered from the originals.
 
+use pyo3::intern;
 use pyo3::prelude::*;
+use pyo3::types::PyDict;
 
 use crate::getenv_use_multiple_threads;
 use faer_ext::{IntoFaerComplex, IntoNdarrayComplex};
@@ -110,6 +112,8 @@ pub fn quantum_volume(
     let num_unitaries = width * depth;
     let mut permutation: Vec<Qubit> = (0..num_qubits).map(Qubit).collect();
 
+    let kwargs = PyDict::new_bound(py);
+    kwargs.set_item(intern!(py, "num_qubits"), 2)?;
     let mut build_instruction = |(unitary_index, unitary_array): (usize, Array2<Complex64>),
                                  rng: &mut Pcg64Mcg|
      -> PyResult<Instruction> {
@@ -118,9 +122,10 @@ pub fn quantum_volume(
             permutation.shuffle(rng);
         }
         let unitary = unitary_array.into_pyarray_bound(py);
+
         let unitary_gate = UNITARY_GATE
             .get_bound(py)
-            .call1((unitary.clone(), py.None(), false))?;
+            .call((unitary.clone(), py.None(), false), Some(&kwargs))?;
         let instruction = PyInstruction {
             qubits: 2,
             clbits: 0,

crates/accelerate/src/split_2q_unitaries.rs

@@ -10,7 +10,9 @@
 // copyright notice, and modified files need to carry a notice indicating
 // that they have been altered from the originals.
 
+use pyo3::intern;
 use pyo3::prelude::*;
+use pyo3::types::PyDict;
 use rustworkx_core::petgraph::stable_graph::NodeIndex;
 
 use qiskit_circuit::circuit_instruction::OperationFromPython;
@@ -27,6 +29,7 @@ pub fn split_2q_unitaries(
     requested_fidelity: f64,
 ) -> PyResult<()> {
     let nodes: Vec<NodeIndex> = dag.op_nodes(false).collect();
+
     for node in nodes {
         if let NodeType::Operation(inst) = &dag.dag()[node] {
             let qubits = dag.get_qargs(inst.qubits).to_vec();
@@ -45,12 +48,14 @@ pub fn split_2q_unitaries(
             if matches!(decomp.specialization, Specialization::IdEquiv) {
                 let k1r_arr = decomp.K1r(py);
                 let k1l_arr = decomp.K1l(py);
+                let kwargs = PyDict::new_bound(py);
+                kwargs.set_item(intern!(py, "num_qubits"), 1)?;
                 let k1r_gate = UNITARY_GATE
                     .get_bound(py)
-                    .call1((k1r_arr, py.None(), false))?;
+                    .call((k1r_arr, py.None(), false), Some(&kwargs))?;
                 let k1l_gate = UNITARY_GATE
                     .get_bound(py)
-                    .call1((k1l_arr, py.None(), false))?;
+                    .call((k1l_arr, py.None(), false), Some(&kwargs))?;
                 let insert_fn = |edge: &Wire| -> PyResult<OperationFromPython> {
                     if let Wire::Qubit(qubit) = edge {
                         if *qubit == qubits[0] {