Add API for shared memory transport

[JEnoch]

zenoh in Rust implement a zero-copy shared memory transport. See examples of use:

• zn_pub_shm.rs
• zn_sub_shm.rs

We need to make this transport also accessible from the zenoh Python API.

[JEnoch]

A use case that popped up recently is the video capture in Python and transport of images to another co-localised Python app.
An open question is: would this be achievable with zero-copy ? I.e. would a video capture library in Python be able to dump images directly in a shared memory buffer allocated by the zenoh's SharedMemory Manager ?

[kydos]

I think that something we should add quickly since there are plenty of uses of openCV in Python and it would be nice for they to leverage zenoh's zero-copy when sharing images across process boundaries. I think the trick is to expose our share memory allocator in such a way that is friendly for use in vision libraries.