Bookworm missing C++20 <format> header

[BsAtHome]

There is a problem in Debian 12 (Bookworm) where gcc-12 is missing the C++20 <format> header. That means that things like the following is not possible:

#include <format>
....
std::string s = std::format("This string {} is at least {} times better.", "formatter", 10);
// formats into: "This string formatter is at least 10 times better."
....

This type of formatting is also the default in python nowadays and is much better than any snprintf or other bodgeworks.

The solution is to add a dependency libfmt-dev for building LinuxCNC to include libfmt (https://github.com/fmtlib/fmt), which is available as packages on all platforms afaik (libfmt7 on bullseye, libfmt9 on bookworm, libfmt10 on trixie; even buster has it).
Using libfmt means that #include <format> with std::format() just needs to be rewritten as #include <fmt/format.h> and use fmt::format().

What do you guys say, is this acceptable?

[rmu75]

std::format only covers part of what is in libfmt -- IME libfmt is a really high quality library that is easy and intuitive to use and really brings benefit to the code.