Add physical qubit support for plain QASM 3 programs

[TheGupta2012]

Bug Fix

Adds support for physical qubit identifiers ($0, $1, …) in plain (non-OpenPulse) QASM 3 programs. Previously, physical qubits were only handled inside OpenPulse contexts; using them in a regular QASM 3 program would either silently mishandle them or raise unexpected errors.

Changes

• Visitor: Detect physical qubit references ($n) in _get_op_bits and register them via the new _register_physical_qubit helper, updating qubit depth tracking and num_qubits automatically.
• Barrier: Allow physical qubit indices on barriers in plain QASM programs instead of rejecting them as invalid pulse qubits.
• Measurement: Route physical qubits in measurement statements through _register_physical_qubit when OpenPulse grammar is not active.
• Analyzer: Update extract_duplicate_qubit to handle both Identifier (physical) and IndexedIdentifier (virtual) qubit types.
• Transformer: Widen transform_gate_qubits qubit map type to accept Identifier | IndexedIdentifier.
• Depth tracking: Extract a _get_qubit_name_and_id helper to unify index extraction for physical and virtual qubits across depth updates and branch-qubit tracking.
• Tests: Add comprehensive test suite for physical qubits covering basic gates, custom gates, barriers, measurements, non-contiguous indices, unrolling, and duplicate detection.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.38462% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/pyqasm/visitor.py	88.88%	5 Missing ⚠️

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