docs: Convert ImageInput-errorchecking examples from docs to tests #6345

Job	Run time
Ubuntu latest releases gcc13 C++20 py3.12 avx2 exr3.2 ocio2.3	7m 10s
Ubuntu bleeding edge gcc14 C++20 py3.12 OCIO/libtiff/exr-main avx2	11m 24s
Ubuntu all local builds gcc12 C++17 avx2 exr3.2 ocio2.3	6m 5s
Ubuntu clang14 C++20 avx2 exr3.1 ocio2.1	7m 54s
VFX2021 gcc9/C++17 py3.7 exr3.1 ocio2.0	5m 57s
VFX2021 clang10/C++17 avx2 exr3.1 ocio2.0	5m 20s
Ubuntu debug gcc9/C++17, sse4.2, exr3.1	11m 17s
VFX2022 gcc9/C++17 py39 exr3.1 ocio2.1	12m 13s
VFX2022 clang13/C++17 py39 avx2 exr3.1 ocio2.1	12m 45s
Ubuntu static libs gcc9 C++17 exr2.4	5m 28s
VFX2022 icc/C++17 py3.9 exr3.1 ocio2.1 qt5.15	10m 15s
Ubuntu clang-format	5m 50s
VFX2022 icx/C++17 py3.9 exr3.1 ocio2.2 qt5.15	9m 41s
VFX2024 sanitizers	33m 54s
VFX2023 gcc11/C++17 py3.10 exr3.1 ocio2.2	11m 30s
macos-12 appleclang13/C++17 py3.10 MacOS-12	1h 12m 46s
VFX2024 gcc11/C++17 py3.11 exr3.2 ocio2.3	12m 30s
macos-13 appleclang14/C++17 py3.11 MacOS-13	19m 19s
VFX2021 oldest gcc9.3/C++17 py3.7 exr-3.1	6m 15s
macos-14 appleclang15/C++20 py3.11 MacOS-14-ARM	6m 51s
windows-2019 VS2019	52m 16s
VFX2021 hobbled gcc9.3/C++17 py3.7 exr-3.1 no-sse	6m 21s
windows-2022 VS2022	48m 48s
VFX2023 abi check	6m 30s
	6h 28m 19s

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