feat: add retry logic on rpc calls, remove unnecessary deps, fix warnings

[wiseaidev]

I haven't tested these changes locally yet, but should work. Let's try it on CI. This PR contains the following changes:

• Async traits have been stabilized and are part of the language since version 1.75: https://blog.rust-lang.org/2023/12/21/async-fn-rpit-in-traits.html
• Removed the unnecessary bincode crate and used serde_json instead
• Added retry logic on RPC calls using backon: https://docs.rs/backon
• Fixed Cargo workspace warnings

[mschneider]

the retry mechanism is not reactive to error codes: a 429 can be retried, but all other errors should probably be exposed to the user immediately. apart from that i would prefer if the retry was implemented outside the core client library functions, if users want to use their own logic.