Cascade key transformation only cascades for one level

[trevorturk]

Describe the bug

Apologies for not testing this myself sooner, but I think we have a bug left over from #220, where transform_keys only cascades for one level.

To Reproduce

Given the following code sample, note that the articles array has the createdAt key, but the comments array has the created_at key, which has not been transformed:

class User
  attr_accessor :created_at, :articles

  def initialize
    @created_at = Time.now
  end
end

class Article
  attr_accessor :created_at, :comments

  def initialize
    @created_at = Time.now
  end
end

class Comment
  attr_accessor :created_at

  def initialize
    @created_at = Time.now
  end
end

class UserResource
  include Alba::Resource

  transform_keys :lower_camel

  attributes :created_at

  association :articles do
    attributes :created_at

    association :comments do
      attributes :created_at
    end
  end
end

user = User.new
comment = Comment.new
article = Article.new
article.comments = [comment]
user.articles = [article]

UserResource.new(user).to_h
# => 
{"createdAt"=>2022-10-24 15:23:10.190596 -0500,
 "articles"=>[{"createdAt"=>2022-10-24 15:23:10.203395 -0500, "comments"=>[{"created_at"=>2022-10-24 15:23:10.198995 -0500}]}]}

[okuramasafumi]

@trevorturk Thank you for reporting, I'll take a look.

[okuramasafumi]

@trevorturk #263 was a solution, but it was hard to debug. I described the problem and solution in the PR description so please check it if you're interested.
In short, there's an implicit requirement that transform_keys should be called before attributes. This might not be a problem for daily development, but in this case it's a trick issue.

[trevorturk]

Ack! Sorry the fix was so difficult, but I did test your PR/branch in my app and everything works as expected! Thank you so much! I have a lot of nested attributes, so this removes a lot of repeated transform_keys keys calls and my resources look much skinnier now :)