ci: break out reusable build steps #3978

Job	Run time
VFX2021 gcc9/C++17 llvm11 py3.7 oiio2.5 sse4 batch-b8avx2	15m 20s
VFX2022 gcc9/C++17 llvm13 py3.9 exr3.1 oiio-rel avx2	17m 2s
VFX2022 clang12/C++17 llvm12 oiio-main py3.9 avx2 batch-avx512	17m 44s
VFX2022 gcc9/C++17 llvm11 py3.9 exr3.1 oiio3.0 sse2 batch-b4sse2	18m 20s
VFX2021 oldest everything gcc9/C++17 llvm9 py3.7 oiio2.5 no-simd	9m 52s
bleeding edge gcc12/C++17 llvm17 oiio/ocio/exr/pybind-main py3.12 avx2 batch-b16avx512 / g++-13 c++17 py3.12	26m 32s
abi check / g++ c++17 py3.10	23m 6s
clang14/C++17 llvm14 py3.8 avx2 batch-b16avx512 / clang++ c++17 py3.8	26m 39s
clang-format / g++ c++17 py3.10	8m 27s
gcc10/C++17 llvm11 oiio-2.5 avx2 / g++-10 c++17 py3.8	11m 21s
Debug gcc7/C++17 llvm11 py3.8 oiio2.5 exr3.1 sse4 / g++-9 c++17 py3.8	27m 41s
icc/C++17 llvm14 py3.9 oiio-main avx2 / icpc c++17 py3.10	36m 2s
icx/C++17 llvm14 py3.10 oiio-3.0 avx2 / icpx c++17 py3.10	27m 3s
latest releases gcc11/C++17 llvm17 oiio-3.0 exr3.2 py3.12 avx2 batch-b16avx512 / g++-13 c++17 py3.12	26m 31s
sanitizers / clang++ c++17 py3.11	35m 6s
VP2023 gcc11/C++17 llvm15 py3.10 oiio-rel avx2 / g++ c++17 py3.10	23m 29s
VP2023 GPU Cuda11 gcc11/C++17 llvm15 py3.10 OIIO-main avx2 / g++ c++17 py3.10	9m 57s
VP2024 gcc11/C++17 llvm17 py3.11 boost1.82 oiio-rel avx2 / g++ c++17 py3.11	27m 51s
MacOS-13-Intel llvm17 / /usr/local/opt/llvm/bin/clang++ c++17 py3.11	20m 12s
MacOS-14-ARM llvm17 / clang++ c++17 py3.11	8m 49s
	6h 57m 4s

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