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.

Merge Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your pull request.

General

• I have read the CONTRIBUTING doc
• I used the commit message format described in CONTRIBUTING
• I have updated any necessary documentation, including READMEs and API docs (if appropriate)

Tests

• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have checked that my tests are not configured for a specific region or account (if appropriate)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[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 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1008   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          135       135           
  Lines         8949      8948    -1     
  Branches      2011      2010    -1     
=========================================
- Hits          8949      8948    -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.