Move AvgPooling external class template declaration out of namespace

include/aidge/operator/AvgPooling.hpp

@@ -102,13 +102,14 @@ inline std::shared_ptr<Node> AvgPooling(
     return AvgPooling(to_array(kernel_dims), name, stride_dims);
 }
 
+
+}  // namespace Aidge
+
 extern template class Aidge::AvgPooling_Op<1>;
 extern template class Aidge::AvgPooling_Op<2>;
 extern template class Aidge::AvgPooling_Op<3>;
 extern template class Aidge::AvgPooling_Op<4>;
 
-}  // namespace Aidge
-
 namespace {
 template <>
 const char *const EnumStrings<Aidge::AvgPoolingAttr>::data[] = {"StrideDims",