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.

[hassec]

Is this feature still planned for the python client?

[swelborn]

I am also interested to see if this is on the roadmap... @hassec @Mallets

[ManuelZ]

Wondering about this as well.

[wyfo]

A first support of the shared memory API has been added in #583. The most important change is that the package is now compiled with shared-memory enabled, allowing zero-copy message sending/reception. However, you still need copies between Rust and Python layers.