feat: Track classical target indices during measurement.

[Altanali]

Issue #, if available:
#1004

Description of changes:
Update the BraketProgramContext to extend the changes introduced in amazon-braket/amazon-braket-default-simulator-python#266, which provide a classical register index to the BraketProgramContext add_measure method when a measurement assignment is used in an OpenQASM program (e.g. b[1] = measure q[1];). This allows translations to and from Braket BDK Circuits and OpenQASM to be consistent with regards to classical register indices used in measurement assignments as currently, these indices are discarded entirely.

Additionally, updating the _measure_targets array in the Circuit object was moved to the add_instruction method from the _add_measure method. This is because users of the Circuit class are able to add measurement instructions via the add_instruction method, but _measure_targets will not be updated to reflect qubits used in the measurement. This results in incorrect behavior when using to_ir to take a circuit with measurements added via add_instruction method calls to OpenQASM as to_ir will check the _measure_targets variable to see if any qubits are measured, see that the list is empty, and apply a measurement to all the qubits in the circuit, including those already measured via the original add_instruction method calls.

Testing done:

A round trip test was added to verify that classical register assignments are persisted when going from BDK Circuit to OpenQASM and back to BDK Circuit via the to_ir and from_ir methods; this is similarly checked when going from OpenQASM to BDK Circuit back to OpenQASM.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (234ab0a) to head (e254410).
Report is 36 commits behind head on main.

Additional details and impacted files

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- Hits          8949      8948    -1     

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