fix(detector): detect builtins attribute replay

[prasannakotyal]

Summary

Targets KG red #185, where custom_kernel stores the first input-derived output on a dynamically named builtins attribute, then returns that same attribute from an input-independent fast path.

This adds a narrow BUILTINS_ATTR_REPLAY detector. It requires:

• an entrypoint setattr(builtins, name, <input-derived call>) mutation
• an input-independent guard over the same builtins attribute, including hasattr(...)
• a replay body containing only getattr(builtins, name) access
• return of that same builtins attribute

Builtins exec/eval dictionary access and other dynamic execution variants stay out of scope.

KernelGuard-Red-Submission: 185

Local verification

• red_69_builtins_attr_replay -> BUILTINS_ATTR_REPLAY, should_filter=True
• red_228_builtins_dict_exec_define stayed valid
• red_229_getattr_builtins_exec_define stayed valid
• red_253_vars_builtins_exec_define stayed valid
• clean fixtures in eval_blue_patch.py stayed valid
• uv run python -m py_compile kernelguard.py

[github-actions]

KernelGuard Blue Evaluation

• Evaluation job: 92
• Blue submission: 65
• Result: passed
• Target red submission caught: True
• Validation suite: TP 20/20, FP 20/20
• Surgicalness score: 1.0
• Workflow run: https://github.com/SinatrasC/kernelguard/actions/runs/25243883536

[SinatrasC]

Thanks for the KernelGuard Flywheel Campaign contribution. We are not merging this narrow variant separately because the consolidated rule-family implementation in #273 is the merge path for this detector area.