fix: remove_idle_qubits(in_place=False) updating qubit count on the wrong module

[ryanhill1]

Summary of changes

Closes #334.

remove_idle_qubits routes every mutation through qasm_module — which is self or a deepcopy depending on in_place — except the qubit-count update at the end of the register loop, which used self. With in_place=False the original module's num_qubits was decremented and the returned copy kept the stale pre-removal count:

m2 = m.remove_idle_qubits(in_place=False)
m2.num_qubits  # 3 (stale — should be 2)
m.num_qubits   # 2 (original mutated — should still be 3)

The copy's AST was already correct (declaration size, operand indices, dumps() output); only the counters were swapped. This also switches the size lookup two lines above from self to qasm_module for consistency — harmless today since the registers are identical at that point, but it keeps the method reading from one object.

Regression test asserts both sides: the returned copy reports the reduced count and dumps the collapsed register, and the original module is left untouched.

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