feat(partition-functions): added framework and some concrete partition functions

GroundState partition function, Rauscher&Thielemann partition function, and composite partition function added

src/network/include/gridfire/partition/partition_rauscher_thielemann.h

@@ -0,0 +1,56 @@
+#pragma once
+
+#include "gridfire/partition/partition_abstract.h"
+
+#include "fourdst/logging/logging.h"
+
+#include <string>
+#include <vector>
+#include <unordered_map>
+#include <array>
+#include <utility>
+
+namespace gridfire::partition {
+    class RauscherThielemannPartitionFunction final : public PartitionFunction {
+    public:
+        RauscherThielemannPartitionFunction();
+        double evaluate(int z, int a, double T9) const override;
+        double evaluateDerivative(int z, int a, double T9) const override;
+        bool supports(int z, int a) const override;
+        std::string type() const override { return "RauscherThielemann"; }
+    private:
+        enum Bounds {
+            FRONT,
+            BACK,
+            MIDDLE
+        };
+    private:
+        struct IsotopeData {
+            double ground_state_spin;
+            std::array<double, 24> normalized_g_values;
+        };
+        struct InterpolationPoints {
+            double T9_high;
+            double G_norm_high;
+            double T9_low;
+            double G_norm_low;
+        };
+        struct IdentifiedIsotope {
+            Bounds bound;
+            const IsotopeData& data;
+            size_t upperIndex;
+            size_t lowerIndex;
+        };
+    private:
+        quill::Logger* m_logger = fourdst::logging::LogManager::getInstance().getLogger("log");
+        std::unordered_map<int, IsotopeData> m_partitionData;
+    private:
+        static InterpolationPoints get_interpolation_points(
+            const size_t upper_index,
+            const size_t lower_index,
+            const std::array<double, 24>& normalized_g_values
+        );
+        IdentifiedIsotope find(int z, int a, double T9) const;
+        static constexpr int make_key(int z, int a);
+    };
+}