fix: emit fresh operand nodes from gate decompositions

[ryanhill1]

Summary of changes

Closes #333. Root-cause fix for the operand-node aliasing behind #331 as well.

Gate decomposition functions in maps/gates.py pass the same qubit operand nodes into every statement they emit (e.g. crz_gate hands qubit1 to two u3_gate and two cx expansions), so the unrolled AST contained IndexedIdentifier objects shared across many statements. Any transformation that rewrites qubit indices in place then mutated a shared node once per referencing statement:

• remove_idle_qubits() walked off its index map → KeyError (remove_idle_qubits() KeyError: unroll() emits aliased operand nodes that _remap_qubits mutates repeatedly #331, point-fixed by the visited-node guard in fix: remove_idle_qubits KeyError on shared operand nodes #332);
• reverse_qubit_order()'s negative-marker pass read an already-marked shared node → KeyError: -1 (reverse_qubit_order() KeyError on aliased operand nodes (same root cause as #331) #333, no guard);
• Decomposer._get_decomposed_gates had the same pattern, so rebase() output was aliased too.

This PR fixes the class of bug at the source: the five statement constructors in maps/gates.py (one_qubit_gate_op, one_qubit_rotation_op, two_qubit_gate_op, ccx_gate_op, global_phase_gate) now deep-copy their qubit operands via a shared _fresh_qubits helper, and Decomposer deep-copies the operands of each rule-emitted gate. Every decomposition composes these constructors, so no emitted statement can share a node with another statement or with the source operation.

With fresh nodes, reverse_qubit_order()'s existing marker logic is correct as-is, and this branch (without #332's guard) independently resolves the #331 repro. #332's guard remains useful belt-and-braces and merges cleanly alongside this.

Verified beyond the test suite: the reversed/remapped crz circuits are unitarily equivalent to the expected reference circuits via qiskit Operator.equiv.

Tests

• test_reverse_qubit_order_gate_decomposition: the reverse_qubit_order() KeyError on aliased operand nodes (same root cause as #331) #333 repro, checked against the full expected unrolled program.
• test_unroll_emits_fresh_operand_nodes: invariant test asserting no two quantum statements share an operand or index node after unroll(), parametrized over crz, crx, c4x, ecr, and inv @ crz.
• test_rebase_emits_fresh_operand_nodes: same invariant for rebase() output.

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