OCaml-Multicore: Lockfree data structures

Computing the size of a concurrent structure is a non-trivial problem. There has been a research paper recently on a lockfree, linearizable size operation on concurrent data structures [Sela, Petrank. 2022].

This PR starts with the implementation of a lock-free set in OCaml, which will be a good first step, and will give an idea of how a size operation can be implementation for more complex data structures.

The set implementation depends on [Maged. 2022].

Project mentor: @Sudha247