Add Rust FFI implementation #11
Description
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.