perf(EigenFunctor): Jacobian Cachine

FOr QSE solving the Jacobian does not change meaninfully between steps.
We have introduced caching so that it does not need to be reevaluated
every step

src/include/gridfire/engine/views/engine_multiscale.h

@@ -670,6 +670,8 @@ namespace gridfire {
              */
             const std::unordered_map<fourdst::atomic::Species, size_t> m_qse_solve_species_index_map;
 
+            mutable std::optional<JacobianType> m_cached_jacobian = std::nullopt;
+
             /**
              * @brief Constructs an EigenFunctor.
              *

src/lib/engine/views/engine_multiscale.cpp

@@ -1091,7 +1091,8 @@ namespace gridfire {
         const double rho
     ) const {
         const fourdst::composition::Composition result = m_baseEngine.collectComposition(comp, T9, rho);
-        fourdst::composition::Composition qseComposition = solveQSEAbundances(result, T9, rho);
+
+        fourdst::composition::Composition qseComposition = getNormalizedEquilibratedComposition(result, T9, rho);
 
         return qseComposition;
     }
@@ -1903,6 +1904,8 @@ namespace gridfire {
             }
         }
 
+        m_cached_jacobian = J_qse; // Cache the computed Jacobian for future use
+
         return 0; // Success
     }