Physical units put in the physical namespace (I am sorry)

test_package/test_package.cpp

@@ -30,6 +30,6 @@ constexpr units::Velocity AUTO avg_speed(units::Length AUTO d, units::Time AUTO
 
 int main()
 {
-  using namespace units::si::literals;
+  using namespace units::physical::si::literals;
   std::cout << "Average speed = " << avg_speed(240.q_km, 2q_h) << '\n';
 }