Delegate missing constants to object class via const_missing

[Copilot]

• Add const_missing to Draper::AutomaticDelegation::ClassMethods to delegate missing constants to the object class when delegate_all is used
• Add tests for the new const_missing behavior
• Update README to document constant delegation via delegate_all
• Update CHANGELOG with new feature entry

Original prompt

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This section details on the original issue you should resolve

<issue_title>Delegate class variable to the decorated object class?</issue_title>
<issue_description>Hello wonderful draper team, here is my use-case, maybe some of you already meet similar issue.

I'd like to allow a decorator class to delegate the class variable access to the parent class, it does not seem to be handled by the delegate_all

for example:

class Car
  WHEELS_COUNT = 4
end

class CarDecorator < ApplicationDecorator
end

car = Car.new
car.class::WHEELS_COUNT => 4

car_decorated = car.decorate
car_decorated.class::WHEEL_NUMBER => uninitialized constant CarDecorator::WHEELS_COUNT (NameError)

Do you have any idea / suggestion about this issue?</issue_description>

Comments on the Issue (you are @copilot in this section)

@Alexander-Senko Delegation in Ruby is meant for methods, not for constants. Every constant belongs to its module/namespace. See [the same question](https://stackoverflow.com/questions/41594617/can-i-use-forwardable-to-delegate-a-constant-in-ruby) for Ruby standard library.

However, that could be implemented using .const_missing. Maybe, I'll do it for my Magic Decorator. But I'm not sure it could be implemented in Draper soon (see the reasons).</comment_new>
<comment_new>@Alexander-Senko

Do you have any idea / suggestion about this issue?

Try something like this (untested) in your ApplicationDecorator:

  def self.const_missing(...) = object_class.const_get(...)

If that works, it could be implemented as a PR. But I don't believe it to be released soon in a new Draper version.</comment_new>

• Fixes Delegate class variable to the decorated object class? #963

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[Alexander-Senko]

Update both README and CHANGELOG.

[Copilot]

Update both README and CHANGELOG.

Done in a2423d2. Added an "Unreleased" section to CHANGELOG and a constant delegation example to the README's "Delegating Methods" section.