feature request: std::print support for boost::system::error_code

[ribbon-otter]

I think it would be nice if boost::system::error_code had std::print support. From analogy of the ostream interface, the std::formatter<boost::system::error_code> would be defined in terms of error_code::to_string() but perhaps we would want to print a more human readable value by default, like error_code::what()

[pdimov]

There's a proposal for adding std::format support to std::error_code:

https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3395r5.html

but it's not finalized or accepted yet.

We probably want to see what the committee will do first, because if we go ahead and add our own, and they later change it, this will break code for our users if we also change to match.

[pdimov]

Although... I suppose that it's reasonably certain by this point that {} should output the same as operator<<, so we can add that at least.