refactor: IWYU updates

test/static/fractional_exponent_quantity.cpp

@@ -22,7 +22,7 @@
 
 #include <mp-units/compat_macros.h>
 #include <mp-units/framework.h>
-#include <mp-units/math.h>
+#include <mp-units/math.h>  // IWYU pragma: keep
 #include <mp-units/systems/isq/electromagnetism.h>
 #include <mp-units/systems/isq/si_quantities.h>
 #include <mp-units/systems/si/units.h>