Parameters and response types

[katspaugh]

I've implemented two SDK calls and the developer experience so far wasn't stellar. 😅

1. Passing parameters is verbose. Why does the client need to know which params are path params and which are query?
2. Response type seems to be buried in a larger FetchResponse type which is also quite verbose.
3. It's not straightforward to match a function and its response type, you have to look in responses -> content.
4. Some functions (e.g. getSupportedFiatCodes) return the data directly, some (e.g. getMasterCopies) wrap it in a { data, error } object. Ideally they should all return the data directly, and errors should be returned as proper HTTP errors.