feat: proper exports implemented for C++ modules

test/static/chrono_test.cpp

@@ -21,15 +21,10 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#include <ratio>
-#ifdef MP_UNITS_MODULES
-#include <chrono>
-import mp_units;
-#else
 #include <mp-units/bits/external/type_traits.h>
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/si/si.h>
-#endif
+#include <ratio>
 
 namespace {