fix: keep acir components missing-witness test valid

[AztecBot]

Fixes the nightly debug build failure from run 30190352077. The public CI dashboard child log is 1785045829822368, and the failing test log is a58e3ea4c384e87e.

Root cause: AcirComponentsCheckTest.DetectsUnconstrainedWitnesses tried to simulate a missing circuit witness by shrinking builder.real_variable_index. In the debug preset, _GLIBCXX_DEBUG catches the resulting internally inconsistent builder before ComponentsChecker reaches its own missing-witness classification: StaticAnalyzer walks the existing gates and indexes witness 10 in a 9-element real_variable_index vector.

Change: keep the builder internally valid, then pass ComponentsChecker a copied ACIR circuit whose graph references witness 999. That still exercises the intended UNCONSTRAINED path, but no longer corrupts the builder object that the shared static analyzer must process.

Validation:

• Reproduced the original failure locally: ./build-debug/bin/acir_components_check_tests --gtest_filter=AcirComponentsCheckTest.DetectsUnconstrainedWitnesses exited 134 with the same _GLIBCXX_DEBUG vector bounds abort.
• cmake --preset debug
• cmake --build build-debug --target acir_components_check_tests
• ./build-debug/bin/acir_components_check_tests --gtest_filter=AcirComponentsCheckTest.DetectsUnconstrainedWitnesses
• ./build-debug/bin/acir_components_check_tests

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Created by claudebox · group: slackbot