catch_exception within a Error set as a potential_error on a LookupArgumentSet does not work

[jimeh]

Error objects which use catch_exception statements, only actually catch the
exception if it is set as a potential_error on a Endpoint.

Within a LookupArgumentSet that specify potential_error, no errors defined by
catch_exception raised within the LookupArgumentSet resolver are caught.

Below is a rough example of the issue:

class Book < Rapid::Object
  field :id, :string
  field :name, :string
end

class TimeoutError < Rapid::Error
  code :timeout_error
  catch_exception Faraday::TimeoutError
end

class BookLookup < Rapid::LookupArgumentSet
  name 'Book Lookup'
  argument :id, :string

  potential_error TimeoutError

  resolver do |set, request, service|
    Faraday.get("http://foo/bar/#{set[:id]}").parsed_body
  end
end

class BookGet < Rapid::Endpoint
  name 'Get book info'

  argument :book, BookLookup, required: true
  field :book, Book

  def call
    book = request.arguments[:book].resolve
    response.add_field :book, book
  end
end

If the BookLookup resolver raises a Faraday::Timeout error, it is not captured
and Rapid returns a unhandled_exception error code instead of the custom
timeout_error.

Adding potential_error TimeoutError on the Endpoint itself fixes the issue,
but obviously it would be better if the LookupArgumentSet resolver captured all
errors relevant to the LookupArgumentSet.