tests: guard native module loading regressions

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Summary

• Add a deterministic source-guard regression test for native VM module loading behavior.
• Register test_native_module_regressions with CTest.

Risky behavior now covered

• com_nativeLibraryExtractPk3 remains default-on, archived, documented, and logged at startup.
• pk3-backed native libraries keep basename-only vm/native_cache/ extraction under fs_homepath/fs_game.
• cached native libraries are reused only after length and CRC checks.
• .so cache writes continue using direct Sys_FOpen/fwrite instead of FS_WriteFile, which rejects native library paths.
• FS_LoadLibrary tries the pk3 cache before loose filesystem paths.
• native VM_Call zero-fills missing vmMain argument slots before invoking DLL entrypoints.

Test files added/updated

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

Why this reduces regression risk

These checks cover recent production-only changes in native module extraction and VM argument passing, both of which affect startup/loading paths for pk3-delivered native modules and can fail only on specific packaging or low-argument native entry calls.

Validation

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