Separate unit/performance CI, optional bounds check

[bugparty]

Summary

• split GitHub Actions into unit tests and performance benchmarks
• add CMake option BITVECTOR_ENABLE_BOUND_CHECK to allow disabling bounds checks
• guard all bounds checks in bitvector.hpp with BITVECTOR_NO_BOUND_CHECK
• skip out-of-range test when bounds checking is disabled

Testing

• cmake -DBITVECTOR_ENABLE_BOUND_CHECK=ON ..
• cmake --build .
• ctest --output-on-failure
• cmake -DBITVECTOR_ENABLE_BOUND_CHECK=OFF ..
• cmake --build .
• ctest --output-on-failure
• ./bitvector_benchmark --benchmark_min_time=0.01s

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https://chatgpt.com/codex/tasks/task_e_68439db78c88832785e40edbe06478ba