[feature] Add fmtlib for faster string formatting

[Bobscorn]

Is your feature request related to a problem? Please describe.
The problem is the speed and convenience of producing formatted strings.
Currently the solution to produce a formatted string is using string concatenating with std::to_string.
For eg. auto desc = "My Position: (" + std::to_string(pos.x) + ", " + std::to_string(pos.y) + ", " + std::to_string(pos.z) + ")";
This is both cumbersome, a little hard to read, and slow (creates 7 + 6 strings just for 1 resulting string).
It also makes it very difficult to specify significant figures or otherwise fine tune number to string conversion.
Currently the only 2 ways I know of how to specify significant figures in using standard equivalents is via sprintf (a C function) or using std::stringstream with std::setprecision, sprintf requires adapter functions while std::stringstream is cumbersome.

Describe the solution you'd like
I propose using fmtlib to ease creation of formatted strings.
This requires bringing fmtlib in as a dependency, and possibly replacing all or some instances of std::to_string with fmtlib equivalents.

Describe alternatives you've considered
2 alternatives considered are writing a wrapper over sprintf to use that for formatted strings, and writing a from-scratch equivalent of formatted strings.
A wrapper over sprintf would work fairly well, would require a set of functions to ensure sprintf works properly in all situations.
However I am inexperienced with writing a performant wrapper over sprintf, so I believe it would lack speed in comparison to fmtlib.
The other alternative of writing an in-house implementation would require a lot of work, and a lot fine tuning to come close to the performance fmtlib claims to offer.

Additional context
Add any other context or screenshots about the feature request here.