feat(mean_field): added initial implementation

note this implementation lacks many tests

libmeanfield/interface/utils/user.cppm

@@ -0,0 +1,36 @@
+module;
+#include <string>
+export module mean_field:utils.user;
+export import :quadrature.policy;
+
+export namespace mean_field::utils {
+    struct potential {
+        double rtol;
+        double atol;
+        int max_iters;
+    };
+
+    struct rot {
+        bool enabled;
+        double omega;
+        double L;
+    };
+
+    struct Args {
+        std::string mesh_file;
+        potential p{};
+        rot r{};
+        bool verbose{};
+        double index{};
+        double mass{};
+        double c{};
+
+        int quad_boost{0};
+
+        int max_iters{};
+        double tol{};
+
+        quadrature::QuadratureOptions quadrature{};
+    };
+
+}