Time types under WTF (MonotonicTime, etc.) add overloads of std::isnan, isinf, and isfinite, but it is generally UB to add declarations&definitions to `namespace std`: https://en.cppreference.com/w/cpp/language/extending_std

Instead, these functions should be class member functions, or free functions outside of `std`.
I don't believe these functions are used in generic code, so I think member functions are more appropriate here.