Keeps the definitions hidden and allows changes to the structs without
needing to recompile all users of classes containing said structs.

Uses a std::string_view instead of a std::string, given the pointed to
string isn't modified and is only used in a formatting operation.

This is nice because a few usages directly supply a string literal to
the function, allowing these usages to otherwise not heap allocate,
unlike the std::string overloads.

While we're at it, we can combine the address formatting into a single
formatting call.