Add Rust FFI implementation

[mpenciak]

If we will be using this Poseidon repository in the main yatima-lang project to hash our Lurk expressions in the scalar store, it will be important to have an efficient version of the Poseidon hash taken from the Rust implementation.

A resolution to this issue should include

• An implementation of Poseidon hash calling the Rust implementation via FFI.
• LSpec tests that ensure the Lean and Rust implementations agree.
• Benchmarks to compare the relative performance gain between the implementations.