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_abstract.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <string>
+
+namespace gridfire::partition {
+    class PartitionFunction {
+    public:
+        virtual ~PartitionFunction() = default;
+        virtual double evaluate(int z, int a, double T9) const = 0;
+        virtual double evaluateDerivative(int z, int a, double T9) const = 0;
+        virtual bool supports(int z, int a) const = 0;
+        virtual std::string type() const = 0;
+    };
+}