Mark more internal functions as `[[nodiscard]]` #473

Job	Run time
clang-format	6s
Windows MSVC Shared Release	2m 0s
Windows MSVC Shared Debug	1m 59s
Windows MSVC Static Release	3m 20s
Windows MSVC Static Debug	2m 35s
Windows ClangCL Shared Release	2m 16s
Windows ClangCL Shared Debug	3m 31s
Windows ClangCL Static Release	4m 51s
Windows ClangCL Static Debug	4m 9s
Windows Clang Shared Release	2m 13s
Windows Clang Shared Debug	1m 21s
Windows Clang Static Release	2m 50s
Windows Clang Static Debug	2m 13s
Linux GCC Shared Release	55s
Linux GCC Shared Debug	1m 22s
Linux GCC Static Release	1m 10s
Linux GCC Static Debug	1m 2s
Linux Clang Shared Release	1m 34s
Linux Clang Shared Debug	43s
Linux Clang Static Release	2m 6s
Linux Clang Static Debug	1m 25s
macOS Clang Shared Release	1m 2s
macOS Clang Shared Debug	1m 10s
macOS Clang Static Release	1m 5s
macOS Clang Static Debug	58s
	47m 56s

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