build

C++20 compatible polyfill for `<expected>` #1041

Job	Run time
macos (Debug, appleclang, 15, cxx20 cxx23)	6s
nixos (gcc)	1m 43s
macos (Debug, clang, 18, 15, cxx20 cxx23)	5s
linux (Debug, gcc, 12, cxx20)	23s
nixos (clang)	2m 35s
macos (Release, appleclang, 15, cxx20 cxx23)	5s
linux (Debug, clang, 16, cxx20)	21s
macos (Release, clang, 18, 15, cxx20 cxx23)	5s
linux (Debug, clang, 17, cxx20)	27s
windows (Debug, Visual Studio 17 2022, 2025, cxx20)	1m 26s
linux (Debug, gcc, 13, cxx20 cxx23)	1m 1s
windows (Release, Visual Studio 17 2022, 2025, cxx20)	1m 27s
linux (Debug, gcc, 14, cxx20 cxx23)	1m 33s
linux (Debug, clang, 18, cxx20 cxx23)	1m 16s
linux (Debug, clang, 19, cxx20 cxx23)	1m 1s
linux (Release, gcc, 12, cxx20)	20s
linux (Release, clang, 16, cxx20)	25s
linux (Release, clang, 17, cxx20)	28s
linux (Release, gcc, 13, cxx20 cxx23)	59s
linux (Release, gcc, 14, cxx20 cxx23)	1m 39s
linux (Release, clang, 18, cxx20 cxx23)	1m 23s
linux (Release, clang, 19, cxx20 cxx23)	1m 1s
	19m 49s

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