Add FoW C++ unit harnesses and sanitizers

[Belzedar94]

Summary

• add C++-backed FoW unit, sanitizer, and benchmark entrypoints wired into the engine via new CLI switches
• expose scripts for FoW unit suites, sanitizer builds, and benchmark comparisons alongside updated guides
• document the expanded coverage and remaining gaps across the implementation and user guides

Testing

• not run (not requested)

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Codex Task