Update cppformat v2 to fmtlib v4

* I did this mainly to remove some build warnings that were showing up
in cppformat v2 underneath clang (the default macOS compiler)
* At this point, WUT will build on macOS with no warnings whatsoever.

tools/readrpl/main.cpp

@@ -1,5 +1,5 @@
 #include <excmd.h>
-#include <format.h>
+#include <fmt/format.h>
 #include <fstream>
 #include <iostream>
 #include <vector>