Currently the loop which writes the data from the fragmented origin to
the destination, moves to the next chunk eagerly after writing the value
of the current chunk, if the current chunk is exhausted.
This presents a problem when we are writing the last piece of data from
the last chunk, as the chunk will be exhausted and we eagerly attempt to
move to the next chunk, which doesn't exist and dereferencing it will
fail. The solution is to not be eager about moving to the next chunk and
only attempt it if we actually have more data to write and hence expect
more chunks.
This commit introduces cell serializers and views based on the in-memory
representation infrastructure. The code doesn't assume anything about
how the cells are stored, they can be either a part of another IMR
object (once the rows are converted to the IMR) or a separate objects
(just like current atomic_cell).
