tests: guard pk3 native library cache behavior

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Summary

• Adds a deterministic regression source guard for pk3-backed native library extraction/cache behavior.
• Registers the guard as test_pk3_native_library_cache in CTest.

Risky behavior now covered

• com_nativeLibraryExtractPk3 remains default-on, archived, documented, and logged at startup.
• pk3 native libraries are cached under vm/native_cache/ using only the basename and the homepath game directory.
• Cache reuse requires matching pk3 CRC, disk length, and disk CRC before attempting to load from cache.
• New extraction keeps the direct write path and warning/extraction logs, and FS_LoadLibrary tries the pk3 cache before loose filesystem paths.

Test files added/updated

• Added tests/scripts/test_pk3_native_library_cache.sh
• Updated CMakeLists.txt

Why this reduces regression risk

This path controls native module loading from .pk3 packages, so mistakes can break standalone/full-conversion UI or game module loading, bypass the intended cache safety checks, or load stale/corrupt extracted libraries. The test guards the security- and compatibility-relevant invariants without requiring game data, a display, or dynamic loader success.

Validation

• tests/scripts/test_pk3_native_library_cache.sh
• cmake -S . -B build-coverage-tests -DBUILD_TESTING=ON -DBUILD_UNIT_TESTS=OFF && ctest --test-dir build-coverage-tests -R test_pk3_native_library_cache --output-on-failure