Build error on OSX with Xcode 16.3

[pcaspers]

I am getting a compile error on OSX with Xcode 16.3.

[build] /Library/Developer/CommandLineTools/SDKs/MacOSX15.4.sdk/usr/include/c++/v1/string:821:42: error: implicit instantiation of undefined template 'std::char_traits<unsigned char>'
[build]   821 |   static_assert(is_same<_CharT, typename traits_type::char_type>::value,
[build]       |                                          ^
[build] /Users/a/repositories/homebrew/include/cpprest/streams.h:79:39: note: in instantiation of template class 'std::basic_string<unsigned char>' requested here
[build]    79 |     static std::basic_string<uint8_t> format(const T& val)
[build]       |                                       ^
[build] /Library/Developer/CommandLineTools/SDKs/MacOSX15.4.sdk/usr/include/c++/v1/__fwd/string.h:23:29: note: template is declared here
[build]    23 | struct _LIBCPP_TEMPLATE_VIS char_traits;
[build]       |                             ^

See here

https://developer.apple.com/documentation/xcode-release-notes/xcode-16_3-release-notes

In particular:

The base template for std::char_traits has been removed. If you are using std::char_traits with types other than char, wchar_t, char8_t, char16_t, char32_t or a custom character type for which you specialized std::char_traits, your code will stop working. The Standard does not mandate that a base template is provided, and such a base template is bound to be incorrect for some types, which could previously cause unexpected behavior while going undetected.

[pcaspers]

duplicates #1812