* Update shared-memory to new version & refactor

This two are combined in a single commit because the new version of
shared-memory doesn't provide the used functionality anymore.

Therefore in order to update the version of this crate we implement the
functionality that we need by ourselves, providing a cleaner API along
the way.

* Significantly decrease the required memory for a workspace

For some reason it was allocating an entire GiB of memory. I suspect
this has something to do with the current memory size limit of a PVF
execution environment (the prior name suggests that). However, we don't
need so much memory anywhere near that amount.

In fact, we could reduce the allocated size even more, but that maybe
for the next time.

* Unlink shmem just after opening

That will make sure that we don't leak the shmem accidentally.

* Do not compile workspace mod for androind and wasm

* Address some review comments

* Fix the test runner

* Fix missed +1 for the attached flag

* Use .expect rather than .unwrap

* Add a rustdoc for the workspace module

* fixup! Use .expect rather than .unwrap

* Add some doc comments to pub members

* Warn on error removing shm_unlink

* Change the alignment implementation

* Fix the comment nit