Fix #580 by using a fixed-point implementation for unit conversions using integer representations #275

Job	Run time
std::format none C++20 Clang-18 Release	5m 52s
std::format none C++20 Clang-18 Debug	5m 47s
std::format none C++23 Clang-18 Release	5m 54s
std::format none C++23 Clang-18 Debug	5m 38s
std::format gsl-lite C++20 Clang-18 Release	6m 0s
std::format gsl-lite C++20 Clang-18 Debug	6m 1s
std::format gsl-lite C++23 Clang-18 Release	5m 54s
std::format gsl-lite C++23 Clang-18 Debug	5m 34s
std::format ms-gsl C++20 Clang-18 Release	6m 16s
std::format ms-gsl C++20 Clang-18 Debug	5m 59s
std::format ms-gsl C++23 Clang-18 Release	5m 43s
std::format ms-gsl C++23 Clang-18 Debug	5m 39s
fmtlib none C++20 Clang-18 Release	5m 36s
fmtlib none C++20 Clang-18 Debug	5m 33s
fmtlib none C++23 Clang-18 Release	5m 37s
fmtlib none C++23 Clang-18 Debug	6m 2s
fmtlib gsl-lite C++20 Clang-18 Release	5m 46s
fmtlib gsl-lite C++20 Clang-18 Debug	5m 53s
fmtlib gsl-lite C++23 Clang-18 Release	5m 43s
fmtlib gsl-lite C++23 Clang-18 Debug	5m 37s
fmtlib ms-gsl C++20 Clang-18 Release	5m 45s
fmtlib ms-gsl C++20 Clang-18 Debug	7m 22s
fmtlib ms-gsl C++23 Clang-18 Release	5m 45s
fmtlib ms-gsl C++23 Clang-18 Debug	5m 56s
	2h 20m 52s

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