Character traits are only standardized for character types of which
std::uint8_t is not. All major C++ implementations happen to define
this specialization but because it is not standard C++ they are
allowed to remove it as LLVM has done by deprecating this specialization
in LLVM 18. It is slated for removal in LLVM 19. To avoid compilation
errors and to get ahead of any deprecation warnings when LLVM 18 ships
we need to define our own std::uint8_t character traits.
SFML 4 will have access to C++20's std::u8string which should let us
remove this code.
