Add SubArray class

This allow to manipulate contiguous sub parts of arrays in the same way as arrays themselves

Note that for performances reasons, SubArray cannot be Array

src/mesh/SubItemValuePerItem.hpp

@@ -61,7 +61,7 @@ class SubItemValuePerItem
 
    public:
     template <typename IndexType>
-    PUGS_INLINE const DataType&
+    PUGS_FORCEINLINE DataType&
     operator[](IndexType i) const noexcept(NO_ASSERT)
     {
       static_assert(std::is_integral_v<IndexType>, "SubView is indexed by integral values");