fix(bb): repair acir components debug regression test

[AztecBot]

Summary

• Fixes the canonical nightly debug failure in run 30190406234, where AcirComponentsCheckTest.DetectsUnconstrainedWitnesses aborted under _GLIBCXX_DEBUG with an out-of-bounds std::vector access.
• The root cause was the regression test corrupting UltraCircuitBuilder::real_variable_index with resize(9). That violates builder invariants, so the static analyzer aborted before ComponentsChecker could report the intended UNCONSTRAINED error.
• Reworks the fixture to compare the full ACIR circuit against a valid synthesized circuit that omits the ACIR witnesses, and adds the checker message to the expected-type assertion for easier future diagnosis.

Notes

The linked aztec-claude run 30190267425 is a separate stale scheduled workflow copy; aztec-claude#2041 already carries that schedule guard. The real current debug-build failure is the canonical aztec-packages run above.

Testing

• cmake --preset debug
• cmake --build --preset debug --target acir_components_check_tests -j$(nproc)
• ./build-debug/bin/acir_components_check_tests --gtest_filter=AcirComponentsCheckTest.DetectsUnconstrainedWitnesses
• ./build-debug/bin/acir_components_check_tests
• NATIVE_PRESET=debug barretenberg/cpp/scripts/run_test.sh acir_components_check_tests AcirComponentsCheckTest.DetectsUnconstrainedWitnesses

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Created by claudebox · group: slackbot · Slack thread