Migrate libfmt to std::format

[ahuston-0]

As std::format is now present in all major compilers, libfmt can be removed.

[ahuston-0]

Clang support is still not quite there yet... need to check this later

[dkrautha]

Besides clang not being there quite yet (its hidden behind an experimental compiler flag), this was only added to the new GCC 13 release very recently, so our build target of Debian 11 in #85 would not have support, as it only has GCC 10.