feat(mean_field): added initial implementation

note this implementation lacks many tests

libmeanfield/interface/utils/domain.cppm

@@ -0,0 +1,24 @@
+module;
+#include <mfem.hpp>
+
+export module mean_field:utils.domain;
+export import :fem;
+export import :mapping.domain_mapper;
+export import :boundary.contexts;
+
+export namespace mean_field::utils {
+
+    bool get_reference_point(
+        const fem::FEM &fem,
+        const mfem::Vector &x_phys_target,
+        mfem::Vector &x_ref
+    );
+
+    double eval_grid_function_at_point(
+        const fem::FEM &fem,
+        const mfem::GridFunction &u,
+        const mfem::Vector &x,
+        mapping::COORDINATE_SPACE vspace = mapping::COORDINATE_SPACE::REFERENCE,
+        mapping::COORDINATE_SPACE rspace = mapping::COORDINATE_SPACE::PHYSICAL
+    );
+}