Fix typelizer options merging in inherited serializers

[Envek]

It should be possible to override individual typelizer options in inherited sertializers:

class BaseSerializer < ActiveModel::Serializer
  include Typelizer::DSL

  typelize plan_id: [:string, comment: "The ID of the plan, which will look like plan_*************"]
end

class ReceiptSerializer < BaseSerializer
  typelize plan_id: [:string, nullable: true]
end

Behavior before this pull request: child serializer definition is ignored altogether

Behavior implemented: options from the whole inheritance chain are used, child options takes precedence (overwriting options from parent serializers)

{ plan_id: [:string, nullable: true, comment: "The ID of the plan, which will look like plan_*************"]