Parser: expand user-defined gate definitions

[tatopenn-cell]

OpenQASM 2.0 gate NAME(params) args { body } definitions were removed and every call to them was left as an unknown gate, so circuits exported by qiskit.qasm2.dumps (adders, composite gates) did not run.

• Definitions are lifted out before block processing and every call is replaced by the body, with formal qubits and parameters substituted; nested definitions are expanded recursively.
• A call with the wrong number of qubits or parameters raises ValueError.

Tests: single definition; nested definitions with parameters (rot(2*t) → rz(π)); arity error; Qiskit's exported CDKMRippleCarryAdder(2) (embedded as text) parsed, run on every basis state and compared with de.add_registers.

Docs: Step 9 on api/parser.md.

[codecov]

Codecov Report

❌ Patch coverage is 95.83333% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
dense_evolution/circuits/parser.py	95.83%	2 Missing ⚠️

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