modularize clients

[augustin-v]

Implement a client for each interaction requiring a different endpoint interaction. There are multiple endpoints(e.g: https://gamma-api.polymarket.com/ , https://data-api.polymarket.com, clob etc...) to interact with Polymarket's different APIs.

Right now we have one ClobClient struct that calls all of them, it would be nicer to have one struct for each interaction and a "general" client struct. Consider adding an api/ folder with gamma.rs, data.rs, clob.rs etc...

(and test it)

[danishxsethi]

quick q: are you trying to backtest (need history + outcomes) or just live prices?
i've got both archived and can share the format if it saves you time.