perf(allocations): reduced overall allocations by 95%, increaseed jacobian applicatin by 2x

This commit uses global pre allocated work space to dramatically reduce memory usage and allocation time

libmeanfield/interface/mapping/prepared_cache.cppm

@@ -0,0 +1,42 @@
+module;
+
+#include <mfem.hpp>
+#include <vector>
+
+export module mean_field:mapping.prepared_cache;
+import :mapping.types;
+
+export namespace mean_field::mapping {
+    // Flat, owning storage for prepared volume contexts. Load into reusable
+    // workspaces: no MFEM buffers or pointer aliases are owned per quadrature
+    // point. The layout retains every public context field without recomputing
+    // inverses or changing the mapper's numerical contract.
+    class VolumeMappingCache {
+    public:
+        void SetSize(
+            int point_count,
+            int dimension
+        );
+        void Store(
+            int point,
+            const VolumeMappingContext &context
+        );
+        void Load(
+            int point,
+            VolumeMappingContext &context
+        ) const;
+        void LoadInverseJacobian(
+            int point,
+            mfem::DenseMatrix &inverse
+        ) const;
+        [[nodiscard]] int GetPointCount() const;
+        [[nodiscard]] int GetDimension() const;
+
+    private:
+        [[nodiscard]] const double *GetPointData(int point) const;
+        std::vector<double> m_data;
+        int m_point_count{0};
+        int m_dimension{0};
+        int m_point_stride{0};
+    };
+} // namespace mean_field::mapping