Modify testrender to work with triangle meshes #3768

Job	Run time
macos-13 C++17 py3.11 MacOS-13 llvm17	23m 30s
Ubuntu Debug gcc7/C++17 llvm9 py3.7 oiio2.3 exr2.4 sse4 exr2.4	24m 43s
macos-14 C++17 py3.11 MacOS-14-ARM llvm17	8m 45s
Ubuntu gcc10/C++17 llvm10 oiio-release avx2	7m 36s
VFX2021 gcc9/C++17 llvm11 py3.7 oiio2.4 sse4 batch-b8avx2	12m 42s
Ubuntu latest releases gcc11/C++17 llvm16 exr3.2 py3.9 avx2 batch-b16avx512	27m 56s
VFX2022 gcc9/C++17 llvm13 py3.9 exr3.1 oiio-rel avx2	14m 28s
Ubuntu bleeding edge gcc12/C++17 llvm17 oiio/ocio/exr/pybind-main py3.10 avx2 batch-b16avx512	13m 8s
VFX2022 clang12/C++17 llvm12 oiio-main py3.9 avx2 batch-avx512	15m 13s
Ubuntu clang14/C++17 llvm14 py3.8 avx2 batch-b16avx512	16m 5s
VFX2022 gcc9/C++17 llvm11 py3.9 exr3.1 oiio2.3 sse2 batch-b4sse2	14m 30s
Ubuntu clang-format	4m 28s
VFX2022 icc/C++17 llvm14 py3.9 oiio-main avx2	16m 42s
VFX2022 icx/C++17 llvm14 py3.9 oiio2.3 avx2	6h 0m 4s
VFX2023 gcc11/C++17 llvm15 py3.10 oiio-rel avx2	15m 16s
VFX2023 GPU Cuda11 gcc11/C++17 llvm15 py3.10 OIIO-main avx2	4m 14s
VFX2024 gcc11/C++17 llvm17 py3.11 boost1.82 oiio-rel avx2	19m 57s
VFX2021 oldest everything gcc9/C++17 llvm9 py3.7 oiio2.3 no-simd	7m 2s
VFX2022 sanitizers	25m 22s
VFX2023 abi check	8m 49s
	10h 40m 30s

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