Version 25.7.0

What's Changed

• Add gul17::null_safe_string(const char*) and gul17::null_safe_string_view(const char*). The new functions construct a string or string_view from a null-terminated C string and are safe against null pointers.
• Allow gul17::join() on ranges of string-like types that do not have a size() member function (e.g. const char*).
• Add gul17::join() overloads for joining ranges of elements with a custom string conversion function.
• Reintroduce gul17::OverloadSet. This class template allows creating an overload set from an arbitrary number of function objects. It was already part of GUL14 and is now included in an updated version with a C++17 template argument deduction guide.