`fmt` formatting errors should be caught at build time, not at run time

[c-dilks]

More recent versions of fmt can do this, but we may need to re-think how Logger is implemented, in particular: https://github.com/JeffersonLab/iguana/blob/05347b2d9bf27a34e5d3844f45f7ad2033b78ce1/src/iguana/services/Logger.h#L119-L122

[c-dilks]

This is somewhat more difficult than expected:

• we are restricted to C++17, so to use fmt's compile-time error catching, we must use its FMT_STRING macro, which only accepts literals; as far as I understand, this means we need our own preprocessor macros. Note that things are easier in C++20
• I tried writing such preoprocessor macro implementation in #267, but after some testing, it makes some generalized log printing rather difficult, and one-line if / else blocks become a bit dodgy (because of handling semicolons and scopes ({ and }))
• We could use a better logging library, but I'm not sure it's a good idea on imposing yet another dependency just for logging; the Logger class exists to avoid another dependency

I'm going to leave this issue open, in case someone has a better idea than #267, or is willing to complete it correctly.