update the chrono C++20 support

Author: noah1510

target_data/Cpp/cppDesktop/include/unit_system_20.hpp.template

@@ -249,8 +249,9 @@ namespace std{
 //add compatibility with std::chrono
 namespace sakurajin{
     namespace unit_system{
-        template<class Rep, class Period = std::ratio<1> >
-        time_si unit_cast(const std::chrono::duration<Rep, Period>& other, auto new_multiplier = 1.0){
+        template<class Rep, class Period = std::ratio<1>, class mult_t = UNIT_SYSTEM_DEFAULT_TYPE>
+            requires std::convertible_to<mult_t, UNIT_SYSTEM_DEFAULT_TYPE>
+        time_si unit_cast(const std::chrono::duration<Rep, Period>& other, mult_t new_multiplier = 1.0){
             auto t = std::chrono::duration_cast<std::chrono::duration<double, std::ratio<1,1>>>(other);
             auto retval = time_si{t.count(), 1};
             return retval.convert_multiplier(new_multiplier);