Error Handling

We will need error classes for each type of error returned by YNAB, along with integrating that into the response handling for each endpoint.

This will likely need to be broken down into smaller tasks.

Start by reviewing the response handling for each YNAB endpoint and cataloging the error types returned by YNAB. Break the work into smaller tasks for defining error classes and integrating them into endpoint responses. Done means each identified YNAB error type has a class and response handling uses those classes consistently.

Written by the indexing model from the issue text.