feat(field-support): added field support system, mid migration

currently the barotope and the pressure force operator are migrated to the new support system

libmeanfield/interface/models/structure/structure_base.cppm

@@ -0,0 +1,37 @@
+module;
+#include <mfem.hpp>
+export module mean_field:model.structure.base;
+export import :eos.base;
+
+export namespace mean_field::models::structure {
+    struct StructureSeed {
+        mfem::Vector radius;
+        mfem::Vector density;
+        mfem::Vector enthalpy;
+
+        double stellarRadius;
+        double centralDensity;
+        double centralEnthalpy;
+    };
+
+    struct StructureSeedRequest {
+        double centralDensity;
+        int radialSampleCount{512};
+    };
+
+    class StructureBase {
+    public:
+        virtual ~StructureBase()                                                                       = default;
+
+        [[nodiscard]] virtual const eos::EquationOfState &equationOfState() const noexcept             = 0;
+
+        [[nodiscard]] virtual double targetMass() const noexcept                                       = 0;
+
+        [[nodiscard]] virtual StructureSeed makeInitialSeed(const StructureSeedRequest &request) const = 0;
+
+        virtual void validate() const                                                                  = 0;
+
+    protected:
+        StructureBase() = default;
+    };
+} // namespace mean_field::models::structure