Extend-errors

[BenoitRanque]

This PR extends errors to allow users of the SDK to set the details json object.

The PR also implements IntoResponse for all the error types, so they can be returned directly from their respective routes.

This means the routes.rs file is removed. Note we add a fetch_metrics function, this contains the logic that used to live in the respective route (this was the only route with logic).

Before merging, I'll move all the error types into their own file, but wanted to keep them as-is for now, so it's easier to see what changed/stayed the same.

You may notice the IntoResponse implementation does not use the to_string method on the error types to add the prefix to the message. This is intentional, that information is conveyed with the status code.

[BenoitRanque]

Note on usage/updating to the new error types

SDK users will need to update their error conversion code.
The following code examples use QueryError but the same pattern applies to all error types.

When converting from your own error types, you are encouraged to implement From<YourErrorType> for QueryError
This allows using the ? operator on any function that returns YourErrorType inside a function that returns QueryError

Error types have utility creation function that are generic over a reference to anything implementing ToString. That includes anything implementing display, including any error types. So these examples are all valid:

QueryError::new_invalid_request(&"some static error string");
QueryError::new_unsupported_operation(&SomeErrorType);

Additionally, each error type has an Other variant that can be created from anything that implements Into<Box<dyn Error>>
This error type corresponds to the 500 status code, so those errors won't be shown to the end user (but will show up in traces I believe?)

That error type is created with the new function on each error type. Example:

let json_string = serde_json::to_string(&underlying_value).map_err(QueryError::new)?;

All error types are initially created without details. Users wishing to add details to a created error should use the with_details method, which takes a json value as argument..

let json_string = serde_json::to_string(&underlying_value).map_err(|err| {
  QueryError::new_invalid_request(&"there was a problem serializing the value")
    .with_details(serde_json::json!({
        "key": "value"
    }))
})?;

[sordina]

Looks good @BenoitRanque I think stepping through with you yesterday cleared everything up for me.

[sordina]

👍