refactor(l2): reduce lines in eth client (#3957)

**Motivation**

Creating a `RpcRequest` required ~6 lines of duplicated code in each
method.
We were also matching on `Result` instead of using the `?` operator.

**Description**

- Adds a `RpcRequest::new()` method.  
- Improves error handling.


Closes None

Author: avilagaston9