Remove troublesome ::ratio members

For some reason, MSVC seems to want to instantiate these, even though
nobody ever asks for them (as evidenced by the fact that the builds
passed on other architectures).

src/core/include/units/bits/equivalent.h

@@ -72,8 +72,8 @@ struct equivalent_impl<D1, D2> :
 // additionally accounts for unknown dimensions
 template<Unit U1, Dimension D1, Unit U2, Dimension D2>
 struct equivalent_unit :
-    std::disjunction<equivalent_impl<U1, U2>, std::bool_constant<U1::ratio / dimension_unit<D1>::ratio ==
-                                                                 U2::ratio / dimension_unit<D2>::ratio>> {};
+    std::disjunction<equivalent_impl<U1, U2>,
+                     std::bool_constant<U1::mag / dimension_unit<D1>::mag == U2::mag / dimension_unit<D2>::mag>> {};
 
 // point origins
 

src/core/include/units/bits/unit_text.h

@@ -151,14 +151,14 @@ constexpr auto unit_text()
       // use predefined coherent unit symbol
       constexpr auto symbol_text = coherent_unit::symbol;
       constexpr auto prefix_txt =
-        prefix_or_ratio_text<U::ratio / coherent_unit::ratio, typename U::reference::prefix_family,
+        prefix_or_ratio_text<as_ratio(U::mag / coherent_unit::mag), typename U::reference::prefix_family,
                              symbol_text.standard().size()>();
       return prefix_txt + symbol_text;
     } else {
       // use derived dimension ingredients to create a unit symbol
       constexpr auto symbol_text = derived_dimension_unit_text<Dim>();
       constexpr auto prefix_txt =
-        prefix_or_ratio_text<U::ratio / coherent_unit::ratio, typename U::reference::prefix_family,
+        prefix_or_ratio_text<as_ratio(U::mag / coherent_unit::mag), typename U::reference::prefix_family,
                              symbol_text.standard().size()>();
       return prefix_txt + symbol_text;
     }

src/core/include/units/chrono.h

@@ -86,13 +86,13 @@ using to_std_ratio = decltype(detail::to_std_ratio_impl<R>());
 template<typename U, typename Rep>
 [[nodiscard]] constexpr auto to_std_duration(const quantity<isq::si::dim_time, U, Rep>& q)
 {
-  return std::chrono::duration<Rep, to_std_ratio<U::ratio>>(q.number());
+  return std::chrono::duration<Rep, to_std_ratio<as_ratio(U::mag)>>(q.number());
 }
 
 template<typename C, typename U, typename Rep>
 [[nodiscard]] constexpr auto to_std_time_point(const quantity_point<clock_origin<C>, U, Rep>& qp)
 {
-  using ret_type = std::chrono::time_point<C, std::chrono::duration<Rep, to_std_ratio<U::ratio>>>;
+  using ret_type = std::chrono::time_point<C, std::chrono::duration<Rep, to_std_ratio<as_ratio(U::mag)>>>;
   return ret_type(to_std_duration(qp.relative()));
 }
 

src/core/include/units/prefix.h

@@ -52,7 +52,6 @@ namespace detail {
 template<PrefixFamily PF, ratio R>
 struct prefix_base : downcast_base<prefix_base<PF, R>> {
   using prefix_family = PF;
-  static constexpr ::units::ratio ratio = R;
   static constexpr Magnitude auto mag = as_magnitude<R>();
 };
 

src/core/include/units/unit.h

@@ -53,7 +53,6 @@ namespace units {
  */
 template<Magnitude auto M, typename U>
 struct scaled_unit : downcast_base<scaled_unit<M, U>> {
-  static constexpr ::units::ratio ratio = as_ratio(M);
   static constexpr Magnitude auto mag = M;
   using reference = U;
 };