qiskit blocks_to_matrix no longer imports

[jordandsullivan]

Describe the bug
There is a function being imported in one of our modified Qiskit transpiler passes which has been deprecated in Qiskit 1.3:

ucc/ucc/transpiler_passes/consolidate_blocks.py

Line 32 in 30039ac

from qiskit._accelerate.convert_2q_block_matrix import blocks_to_matrix

which is used in on line 131 in the following code snippet to convert blocks of the DAGCircuit into matrix form:

ucc/ucc/transpiler_passes/consolidate_blocks.py

Lines 120 to 136 in 30039ac

	if len(block_qargs) > 2:
	q = QuantumRegister(len(block_qargs))
	qc = QuantumCircuit(q)
	if block_cargs:
	c = ClassicalRegister(len(block_cargs))
	qc.add_register(c)
	for nd in block:
	qc.append(nd.op, [q[block_index_map[i]] for i in nd.qargs])
	unitary = UnitaryGate(Operator(qc), check_input=False)
	else:
	try:
	matrix = blocks_to_matrix(block, block_index_map)
	except QiskitError:
	# If building a matrix for the block fails we should not consolidate it
	# because there is nothing we can do with it.
	continue
	unitary = UnitaryGate(matrix, check_input=False)

This blocks_to_matrix function has been deprecated in Qiskit 1.3 (although it is not listed in the Release notes since qiskit._accelerate is not a module part of the official API (it is a Rust wrapper).

We need to find a replacement for this function.

To Reproduce
Steps to reproduce the behavior:

pip install --upgrade qiskit
Installing collected packages: qiskit
  Attempting uninstall: qiskit
    Found existing installation: qiskit 1.2.4
    Uninstalling qiskit-1.2.4:
      Successfully uninstalled qiskit-1.2.4
Successfully installed qiskit-1.3.0
(bench) pytest ucc/tests/test_compile.py
ucc/transpiler_passes/__init__.py:5: in <module>
    from .consolidate_blocks import ConsolidateBlocks
ucc/transpiler_passes/consolidate_blocks.py:32: in <module>
    from qiskit._accelerate.convert_2q_block_matrix import blocks_to_matrix
E   ModuleNotFoundError: No module named 'qiskit._accelerate.convert_2q_block_matrix'; 'qiskit._accelerate' is not a package

Expected behavior
It should convert the blocks to matrix form using the appropriate API.

Additional context
Arguably should consider eliminating or replacing other references to qiskit._accelerate in UCC, given that this is intended as an internal function and likely to be a more fragile part of the API.