Fix various CUDA memory leaks

This MR fixes various CUDA memory leaks.

Operators/BwdTrans/BwdTransCUDA.cu

@@ -7,4 +7,4 @@ std::string OperatorBwdTransImpl<double, ImplCUDA>::className =
     GetOperatorFactory<double>().RegisterCreatorFunction(
         "BwdTransCUDA", OperatorBwdTransImpl<double, ImplCUDA>::instantiate,
         "...");
-}
+} // namespace Nektar::Operators::detail