fix: avoid debug checker crash on failed circuits

[AztecBot]

Summary

• Skip CircuitChecker::check in Chonk debug logging when the incoming circuit has already recorded a builder failure, so the original circuit.err() is reported instead of running a secondary structural check on invalid state.
• Run the ACIR components static analyzer on a bounds-safe builder copy when real_variable_index is shorter than the variables vector, while preserving the original builder for witness classification so missing witnesses still report UNCONSTRAINED.
• Ignore range-list entries whose witness index no longer has a real-variable mapping.

Root Cause

The nightly debug build runs with libstdc++ debug checks enabled. The ACIR components checker can inspect intentionally failed or corrupted builders, including the existing DetectsUnconstrainedWitnesses regression path where real_variable_index is truncated. cdg::StaticAnalyzer_ indexes real_variable_index while walking all builder variables, so debug-mode vector bounds checks abort before the checker can classify the witness as unconstrained.

Chonk's debug-only logging made the same class of issue easier to hit by calling CircuitChecker::check(circuit) before checking circuit.failed(). For a circuit that had already failed during construction, the debug logging could run a second checker over invalid builder state and mask the useful builder error.

Original failed CI run: https://github.com/AztecProtocol/barretenberg-claude/actions/runs/29675727468

Testing

• clang-format-20 -i barretenberg/cpp/src/barretenberg/acir_components_check/components_check.cpp barretenberg/cpp/src/barretenberg/chonk/chonk.cpp
• cmake --build --preset debug --target acir_components_check_tests chonk_tests from barretenberg/cpp
• NATIVE_PRESET=debug barretenberg/cpp/scripts/run_test.sh acir_components_check_tests AcirComponentsCheckTest.DetectsUnconstrainedWitnesses
• NATIVE_PRESET=debug barretenberg/cpp/scripts/run_test.sh acir_components_check_tests AcirComponentsCheckTest.*
• NATIVE_PRESET=debug barretenberg/cpp/scripts/run_test.sh chonk_tests ChonkTests.Basic

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Created by claudebox · group: slackbot

[AztecBot]

Automatically closing this stale claudebox draft PR (no updates for 5+ days). Re-open if still needed.