feature: add barrier instruction support

[rmshaffer]

Issue #, if available:

Description of changes:

Adds a barrier() instruction so that AutoQASM programs can emit OpenQASM barrier compiler directives, matching the Braket SDK's Circuit.barrier() instruction.

Testing done:

Merge Checklist

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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)
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a962209) to head (217207b).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #108   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           52        52           
  Lines         2279      2289   +10     
  Branches       266       265    -1     
=========================================
+ Hits          2279      2289   +10     

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