feat: make possible to sign transactions without state machine

[Dmitry-Borodin]

Purpose

1. Make it possible to get and sign transactions without state machine - last peace why we need it
2. Remote state machine from rust and clients

Scope

Looks like it's doable job, work in progress.
Need to cleanup and maybe move signing logic to another crate when it's working.

Added API last peace of state-machine used

pub fn sign_transaction(
pub fn get_transaction(

TODOs

• finish signing - it's in comments what should be done there
• Move signing logic to more appropriate place
• describe api with uniffi
• adopt android and remove state machine
• adopt ios and remove state machine
• remove state machine from rust

Discussion

Move signing logic from lib.rs, where?