feat(sdk) Remove LinkedChunkListener.

This patch is a turn around about the `LinkedChunkListener`. Many
patches have been removed because `LinkedChunkListener` needed to
support I/O, so errors and async code. The whole code was affected by
that, resulting in a complex API. The idea of this patch is to decoupled
this. Here is how.

First off, `LinkedChunkListener` is removed. So it's one less generic
parameter on `LinkedChunk`. It's also one less trait, so less
implementations.

Second, now `LinkedChunk` accumulates/collects all “updates” under the
form of a new enum `LinkedChunkUpdate`. These updates can be read with
`LinkedChunk::updates(&mut self) -> &Vec<LinkedChunkUpdate>`. The reader
can simply read them, or even drain them. The reader is responsible
to handle these updates and to dispatch them in a storage or whatever.
`LinkedChunk` is no longer responsible to do that, removing the need to
support errors and to be async.

Third, the simplification has led to an optimisation by introducing a
new type `LinkedChunkLinks`. The documentation explains what it does
and why it was needed. The benefit of this type is: it doesn't increase
the size of `LinkedChunk`, but it simplifies the code: no more `Arc`,
no more `Mutex` (it was required because with I/O and async), no more
borrow checker trick, and the code stays as safe as before.