v2 overhaul

[ishandhanani]

This PR starts the journey of overhauling this repo to work with Rubicon V2. This will be a slow and steady process as I continue adding in features. Here's a rough plan of how I want to build this

1. Start implementing the contracts in Rust following rubi-py. This starts with creating a base_contract class and then creating the erc20, market, and router contracts. This should serve as an MVP for this repo as it can allow other Rust devs to use these contracts and build their trading frameworks on top
2. Overhauling RubiconSession with a Client style framework again following the groundwork of rubi-py

Let's see how this goes. Goal is to become a full Rusteacean 🦀 after finishing this