refactor: 💥 basic_concepts, quantity and quantity_cast refactored

BREAKING CHANGE:  ScalableNumber renamed to QuantityValue

Resolves #107

docs/design/quantity.rst

@@ -11,7 +11,7 @@ Interface
 The difference is that it uses ``double`` as a default representation and has
 a few additional member types and functions::
 
-    template<Dimension D, UnitOf<D> U, ScalableNumber Rep = double>
+    template<Dimension D, UnitOf<D> U, QuantityValue Rep = double>
     class quantity {
     public:
       using dimension = D;
@@ -27,7 +27,7 @@ a few additional member types and functions::
     [[nodiscard]] constexpr Quantity auto operator*(const quantity<D1, U1, Rep1>& lhs,
                                                     const quantity<D2, U2, Rep2>& rhs);
 
-    template<ScalableNumber Value, typename D, typename U, typename Rep>
+    template<QuantityValue Value, typename D, typename U, typename Rep>
       requires std::magma<std::ranges::divided_by, Value, Rep>
     [[nodiscard]] constexpr Quantity auto operator/(const Value& v,
                                                     const quantity<D, U, Rep>& q);