perf(GraphEngine): more caching

Added more agressive caching, regained about another 50% performance gain. Solar model over 10Gyr now takes roughly 400ms (as opposed to 1 second before)

src/include/gridfire/engine/engine_graph.h

@@ -882,6 +882,7 @@ namespace gridfire::engine {
         mutable CppAD::ADFun<double> m_epsADFun; ///< CppAD function for the energy generation rate.
         mutable CppAD::sparse_jac_work m_jac_work; ///< Work object for sparse Jacobian calculations.
         mutable std::vector<double> m_local_abundance_cache;
+        mutable std::unordered_map<size_t, StepDerivatives<double>> m_stepDerivativesCache;
 
         bool m_has_been_primed = false; ///< Flag indicating if the engine has been primed.
 

src/include/gridfire/utils/hashing.h

@@ -3,6 +3,7 @@
 #include <cstdint>
 #include <functional>
 
+#include "fourdst/composition/utils/composition_hash.h"
 #include "gridfire/exceptions/exceptions.h"
 #include "gridfire/reaction/reaction.h"
 
@@ -69,4 +70,21 @@ namespace gridfire::utils {
         seed ^= hasher(v) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
         return seed;
     }
+
+    inline std::size_t hash_state(
+        const fourdst::composition::CompositionAbstract& comp,
+        const double T9,
+        const double rho,
+        const reaction::ReactionSet& reactions
+    ) noexcept {
+        constexpr std::size_t seed = 0;
+        std::size_t comp_hash = fourdst::composition::utils::CompositionHash::hash_exact(comp);
+        for (const auto& reaction : reactions) {
+            comp_hash = hash_combine(comp_hash, hash_reaction(*reaction));
+        }
+        std::size_t hash = hash_combine(seed, comp_hash);
+        hash = hash_combine(hash, std::bit_cast<std::size_t>(T9));
+        hash = hash_combine(hash, std::bit_cast<std::size_t>(rho));
+        return hash;
+    }
 }