tests: guard renderer frame wrapping

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Summary

• Add a deterministic renderer source guard for MD3, MDR, and IQM frame wrapping paths.
• Register test_renderer_frame_wrap_guards with CTest and document it in tests/README.md.

Risky behavior now covered

• Frame wrapping must verify positive frame counts before modulo to prevent divide-by-zero regressions.
• Invalid current/old animation frames must reset before frame-indexed culling/draw work.
• IQM backend surface animation must fall back to frame 0 when num_frames is zero.
• Mirrored OpenGL/Vulkan renderer files under both src/renderers and src/platform/renderers stay in sync.

Test files added/updated

• Added tests/scripts/test_renderer_frame_wrap_guards.py
• Updated CMakeLists.txt
• Updated tests/README.md

Why this reduces regression risk

Recent renderer fixes touched edge-case animation frame wrapping in duplicated renderer code. These checks are fast, deterministic, do not require GPU/game data, and pin the ordering that prevents modulo-by-zero and out-of-bounds frame access regressions.

Validation

• python3 tests/scripts/test_renderer_frame_wrap_guards.py /workspace
• cmake -S . -B build-coverage-tests -DBUILD_TESTING=ON -DBUILD_UNIT_TESTS=OFF && ctest --test-dir build-coverage-tests -R test_renderer_frame_wrap_guards --output-on-failure