feat(mean_field): added dimensions, discritization, and start of eos

The full rewrite of mean_field into something maintainable is progressing. dimensions is mostly done, discritization (domain, blocks, and fields) is done, and eos is progressing quickly

src/include/serif/discretization/domain/schema/utils.hpp

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <mfem.hpp>
+
+#include "serif/discretization/domain/concepts.hpp"
+#include "serif/discretization/domain/schema/concepts.hpp"
+
+namespace serif::discretization::domain::schema {
+    // Build the 0/1 marker array MFEM wants when an integrator or an essential
+    // BC should apply only on part of the mesh.
+    template <IsDomainOrSet DomainT, IsSchema SchemaT>
+    [[nodiscard]] mfem::Array<int> make_attribute_marker(const mfem::Mesh &mesh) {
+        static_assert(
+            SchemaT::template contains_domain<DomainT>(),
+            "Requested marker domain is not completely registered in the supplied DomainSchema."
+        );
+
+        mfem::Array<int> marker(mesh.attributes.Max());
+        for (int domainID = 1; domainID <= marker.Size(); ++domainID) {
+            marker[domainID - 1] = SchemaT::template domain_id_belongs_to<DomainT>(domainID) ? 1 : 0;
+        }
+        return marker;
+    }
+}