refactor: 💥 basic_concepts, quantity and quantity_cast refactored

BREAKING CHANGE:  ScalableNumber renamed to QuantityValue

Resolves #107

example/measurement.cpp

@@ -114,15 +114,13 @@ private:
   value_type uncertainty_{};
 };
 
-static_assert(units::ScalableNumber<measurement<double>>);
-
 }  // namespace
 
-template<typename T>
-inline constexpr bool units::treat_as_floating_point<measurement<T>> = std::is_floating_point_v<T>;
 
 namespace {
 
+static_assert(units::QuantityValue<measurement<double>>);
+
 void example()
 {
   using namespace units::physical;