Added FIXME notes for the getSerializationType methods in segments

src/TNL/Algorithms/Segments/BiEllpack.hpp

src/TNL/Algorithms/Segments/BiEllpackView.hpp

src/TNL/Algorithms/Segments/CSR.hpp

src/TNL/Algorithms/Segments/CSRView.hpp

src/TNL/Algorithms/Segments/ChunkedEllpack.hpp

src/TNL/Algorithms/Segments/ChunkedEllpackView.hpp

src/TNL/Algorithms/Segments/Ellpack.hpp

src/TNL/Algorithms/Segments/EllpackView.hpp

src/TNL/Algorithms/Segments/SlicedEllpack.hpp

src/TNL/Algorithms/Segments/SlicedEllpackView.hpp