Fix double-unroll ValidationError when consolidate_qubits=True

[TheGupta2012]

Bug Fix — Fix double-unroll crash when consolidate_qubits=True

Calling module.unroll(consolidate_qubits=True) twice on the same QasmModule raised a ValidationError because consolidate_qubit_registers() was mutating AST nodes in-place. Since self._statements holds a reference to the original program.statements, these mutations corrupted the source AST. On the second unroll, the visitor encountered barrier qubits named __PYQASM_QUBITS__[...] that did not exist in the fresh scope.

Closes #296.

Changes

• Deep-copy: Added unrolled_stmts = deepcopy(unrolled_stmts) at the entry of consolidate_qubit_registers in src/pyqasm/transformer.py, so all in-place identifier renames operate on isolated copies and the original AST remains intact for re-processing.

Reproduction

from pyqasm import loads

qasm3_string = """OPENQASM 3.0;
include "stdgates.inc";
qubit[2] q;
qreg q2[3];
barrier q2;
barrier q, q2;
"""
mod = loads(qasm3_string)
mod.unroll(consolidate_qubits=True)
mod.unroll(consolidate_qubits=True)  # Previously raised ValidationError

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📒 Files selected for processing (3)

• CHANGELOG.md
• src/pyqasm/transformer.py
• tests/qasm3/test_device_qubits.py

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