fix: pass barretenberg debug checks

[AztecBot]

Summary

• keep the unconstrained-witness ACIR test from corrupting the builder's witness map while still removing the synthesized arithmetic gate it wants to test
• ignore stale range-list variable indices instead of letting debug STL bounds checks abort diagnostics
• preserve optional CHECK_CIRCUIT_STACKTRACES data across execution-trace block copies/moves and make missing trace printing a no-op

Root Cause

The debug build exposed two diagnostic-path issues. AcirComponentsCheckTest.DetectsUnconstrainedWitnesses simulated an unconstrained witness by shrinking builder.real_variable_index, leaving existing range-list entries pointing past the end of the vector; libstdc++ debug checks aborted before the components checker could report the intended error.

After that was fixed, ChonkTests.AppPairingInputsTamperingFailure hit a second debug-only path: circuit-checker diagnostics copied execution trace blocks without copying their optional stack traces, then tried to print a row's missing stack trace and threw std::out_of_range.

Verification

• cmake --build barretenberg/cpp/build-debug --target acir_components_check_tests chonk_tests
• barretenberg/cpp/build-debug/bin/acir_components_check_tests
• barretenberg/cpp/build-debug/bin/chonk_tests --gtest_filter=ChonkTests.AppPairingInputsTamperingFailure
• barretenberg/cpp/build-debug/bin/chonk_tests --gtest_filter='ChonkTests.AppPairingInputsTamperingFailure:All/KernelIOTamperingTests.CausesVerificationFailure/*'
• NATIVE_PRESET=debug AVM=0 AVM_TRANSPILER=0 ./barretenberg/cpp/bootstrap.sh build_native
• NATIVE_PRESET=debug AVM=0 AVM_TRANSPILER=0 ./barretenberg/cpp/bootstrap.sh test (6,987 tests in 1,292s)

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Created by claudebox · group: slackbot