fix: Skip rvalue evaluation for MCM-dependent assignment

[aniksd-braket]

When a classical assignment has an MCM-dependent rvalue and the context has no active simulation paths (e.g., Qiskit circuit-building contexts), skip evaluating the rvalue and just propagate MCM-dependency. This prevents NameError when measurement results have no stored runtime value.

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Description of changes:

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b9e18eb) to head (5f4785d).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #377   +/-   ##
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  Coverage   100.00%   100.00%           
=========================================
  Files           49        49           
  Lines         4879      4882    +3     
  Branches       560       561    +1     
=========================================
+ Hits          4879      4882    +3     

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