feat(quadrature): quadrature system brought over

Ported and dramatically cleaned up the quadrature system. This includes centralizing all field definitions

src/include/serif/discretization/domain/concepts.hpp

@@ -1,6 +1,11 @@
 #pragma once
 
 #include <cstddef>
+#include <string_view>
+#include <span>
+#include <array>
+#include <format>
+#include <numeric>
 
 #include "serif/discretization/domain/types.hpp"
 #include "serif/utils/misc/std_helper/cleaning.hpp"
@@ -17,10 +22,33 @@ namespace serif::discretization::domain {
     concept IsBoundary = AIsBaseClassOfB<T, Boundary>;
 
     // A DomainSet is several volumes treated as one. StellarDomains
-    // (core + envelope) is the motivating example.
+    // (core + envelope) is a motivating example.
     template <IsDomain... DomainTs>
     struct DomainSet {
         static constexpr std::size_t count = CountVariadicArguments<DomainTs...>();
+
+        static inline const std::array<std::string_view, count> names{
+            DomainTs::name...
+        };
+    };
+
+    // Do not make the constructors of this class explicit. We want to be able to pass a single domain or a domain set to functions that take a DomainOrSet.
+    class DomainOrSet final {
+    public:
+        template <IsDomain DomainT>
+        // ReSharper disable once CppNonExplicitConvertingConstructor
+        constexpr DomainOrSet(DomainT) noexcept : m_domains(&DomainT::name, 1) {}
+
+        template <IsDomain... DomainTs>
+        // ReSharper disable once CppNonExplicitConvertingConstructor
+        constexpr DomainOrSet(DomainSet<DomainTs...>) noexcept : m_domains(DomainSet<DomainTs...>::names) {}
+
+        [[nodiscard]] constexpr std::span<const std::string_view> domains() const noexcept {
+            return m_domains;
+        }
+
+    private:
+        std::span<const std::string_view> m_domains;
     };
 
     template <IsBoundary... BoundaryTs>
@@ -53,3 +81,25 @@ namespace serif::discretization::domain {
     template <typename BoundaryT, typename BoundaryIDT>
     concept BoundaryIsIdentifiedBy = utils::misc::std_helper::SameType<BoundaryT, typename BoundaryIDT::boundary_type>;
 }
+
+template <>
+struct std::formatter<serif::discretization::domain::DomainOrSet> : std::formatter<std::string_view> {
+    template <typename FormatContext>
+    auto format(const serif::discretization::domain::DomainOrSet& dos, FormatContext& ctx) const {
+        auto join = [&](std::span<const std::string_view> strings, std::string_view delimiter) {
+            return std::accumulate(
+                strings.begin(),
+                strings.end(),
+                std::string{},
+                [delimiter](std::string acc, std::string_view s) {
+                    if (!acc.empty()) {
+                        acc += delimiter;
+                    }
+                    acc += s;
+                    return acc;
+                }
+            );
+        };
+        return std::formatter<std::string_view>::format(std::format("DomainOrSet(domains=[{}])", join(dos.domains(), ", ")), ctx);
+    }
+};