fix: shallow-copy circuit instructions into initial branched path

[rmshaffer]

Issue #, if available:
Fixes #370

Description of changes:

The initial branched SimulationPath was seeded with shared references to Circuit.instructions, so the contiguous-qubit remapping in BaseLocalSimulator._map_circuit_qubits silently retargeted the path's gates and corrupted the final state whenever the circuit's qubit set was non-contiguous. Shallow-copying each instruction into the initial path keeps the two lists independent.

Testing done:

Added two regression tests in TestMCMNonContiguousClassicalIndices covering the minimal repro and the non-monotonic c[N] case; both fail on main and pass with the fix. All tests pass.

Merge Checklist

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (1d8fcea) to head (515fd36).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #371   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           49        49           
  Lines         4884      4885    +1     
  Branches       562       562           
=========================================
+ Hits          4884      4885    +1     

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