Add numberOf template functions

These functions return the number of items (template parameter)

src/mesh/Connectivity.hpp

@@ -609,6 +609,23 @@ class Connectivity final : public IConnectivity
     return cell_to_node_matrix.numRows();
   }
 
+  template <ItemType item_type>
+  PUGS_INLINE size_t
+  numberOf() const
+  {
+    if constexpr (item_type == ItemType::cell) {
+      return this->numberOfCells();
+    } else if constexpr (item_type == ItemType::face) {
+      return this->numberOfFaces();
+    } else if constexpr (item_type == ItemType::edge) {
+      return this->numberOfEdges();
+    } else if constexpr (item_type == ItemType::node) {
+      return this->numberOfNodes();
+    } else {
+      static_assert(is_false_item_type_v<item_type>, "unknown ItemType");
+    }
+  }
+
   CellValue<const double>
   invCellNbNodes() const
   {

src/mesh/Mesh.hpp

@@ -63,6 +63,13 @@ class Mesh final : public IMesh
     return m_connectivity->numberOfCells();
   }
 
+  template <ItemType item_type>
+  PUGS_INLINE size_t
+  numberOf() const
+  {
+    return m_connectivity->template numberOf<item_type>();
+  }
+
   PUGS_INLINE
   const NodeValue<const Rd>&
   xr() const