Use FetchContent for robin-map #51

Job	Run time
macos-13 C++17 py3.11 MacOS-13 llvm17	5m 23s
Ubuntu Debug gcc7/C++14 llvm9 py2.7 oiio2.3 exr2.4 sse4 exr2.4	2m 4s
macos-14 C++17 py3.11 MacOS-14-ARM llvm17	5m 55s
Ubuntu gcc10/C++17 llvm10 oiio-release exr2.5 avx2	1m 58s
VFX2019 gcc6/C++14 llvm9 py2.7 exr2.4 oiio2.3 sse2	6m 22s
Ubuntu latest releases gcc11/C++17 llvm16 exr3.2 py3.9 avx2 batch-b16avx512	16m 17s
VFX2019 clang9/C++14 llvm9 oiio-release avx2 exr2.4 py2.7	6m 51s
Ubuntu bleeding edge gcc12/C++17 llvm17 oiio/ocio/exr/pybind-master py3.10 avx2 batch-b16avx512	21m 48s
VFX2020 gcc6/C++14 llvm10 py3.7 exr2.4 oiio2.2 sse4	5m 40s
Ubuntu clang14/C++17 llvm14 exr3.1 py3.8 avx2 batch-b16avx512	17m 33s
VFX2021 gcc9/C++17 llvm11 py3.7 exr2.5 oiio2.3 avx2 batch-b8avx2	5m 54s
Ubuntu clang-format	1m 52s
VFX2022 gcc9/C++17 llvm13 py3.9 exr3.1 oiio-rel avx2	5m 40s
VFX2022 clang12/C++17 llvm12 oiio-master exr3.1 py3.9 avx2 batch-avx512	5m 9s
VFX2022 icc/C++17 llvm14 py3.9 exr3.1 oiio-master avx2	9m 41s
VFX2022 icx/C++17 llvm14 py3.9 exr3.1 oiio2.3 avx2	8m 33s
VFX2023 gcc11/C++17 llvm15 py3.10 exr3.1 oiio-rel avx2	11m 34s
VFX2023 GPU Cuda11 gcc11/C++17 llvm15 py3.10 exr3.1 OIIO-master avx2	9m 29s
VFX2019 oldest everything gcc6/C++14 llvm9 py2.7 oiio2.3 no-simd exr2.4	6m 17s
VFX2022 sanitizers	5m 21s
VFX2023 abi check	8m 17s
	2h 47m 38s

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