cleanup: Make span use unsized-agnostic #7788

Job	Run time
macos-12 appleclang13/C++17 py3.10 MacOS-12	1m 36s
Ubuntu latest releases gcc12 C++17 avx2 exr3.2 ocio2.3	1s
macos-13 appleclang14/C++17 py3.11 MacOS-13	1m 35s
windows-2019 VS2019	1m 31s
Ubuntu bleeding edge gcc14 C++20 py3.12 OCIO/libtiff/exr-master avx2	1m 36s
VFX2021 gcc9/C++17 py3.7 exr3.1 ocio2.0	1s
macos-14 appleclang15/C++20 py3.11 MacOS-14-ARM	1s
windows-2022 VS2022	1m 27s
Ubuntu clang14 C++20 avx2 exr3.1 ocio2.1	1m 36s
VFX2021 clang10/C++14 avx2 exr3.1 ocio2.0	1s
Ubuntu debug gcc9/C++17, sse4.2, exr3.1	2s
VFX2022 gcc9/C++17 py39 exr3.1 ocio2.1	1s
Ubuntu static libs gcc9 C++17 exr2.4	1s
VFX2022 clang13/C++17 py39 avx2 exr3.1 ocio2.1	1s
Ubuntu clang-format	59s
VFX2022 icc/C++17 py3.9 exr3.1 ocio2.1 qt5.15	1s
VFX2022 icx/C++17 py3.9 exr3.1 ocio2.1 qt5.15	1s
VFX2022 sanitizers	1s
VFX2023 gcc11/C++17 py3.10 exr3.1 ocio2.2	1s
VFX2024 gcc11/C++17 py3.11 exr3.2 ocio2.3	1s
VFX2021 oldest/hobbled gcc9.3/C++17 py3.7 exr-3.1 no-sse no-ocio	1s
VFX2023 abi check	35s
	11m 10s

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