feat(discretization): Added SystemLayout and associated helpers to allow for more robust access to parts of the block system

src/include/serif/discretization/blocks/keys.hpp

@@ -0,0 +1,16 @@
+#pragma once
+
+/**
+ * @file keys.hpp
+ * @author Emily M. Boudreaux
+ *
+ * @brief Keys for the shared layout of a discretized state and residual in a block-structured system.
+ */
+
+
+namespace serif::discretization::blocks::keys {
+    /**
+     * @brief Share one independently ordered state and residual layout across numerical services.
+     */
+    struct Layout final {};
+}