Support for config inheritance

[sobakasu]

Some of our projects (glg, gus, nfsa-pro) use Collections::Base with inheritance. They define an 'ApplicationCollection' with common settings and then inherit from that. Example code:

class ApplicationCollection < Katalyst::Tables::Collection::Base
  config.paginate = {}
end

class SomeController
  class Collection < ApplicationCollection
    # controller specific settings
  end
end

The expectation being that config in ApplicationCollection is inherited by SomeController::Collection. That doesn't seem to happen, as we use a class variable @config which is not inherited. This PR changes @config to a class_attribute, and dups it for subclasses. And added some tests.

[sfnelson]

This change makes sense but it's a response to a wider deprecation of ActiveSupport::Configurable in Rails 8.1. I took a 'light' approach in this plus the other gems like content and koi, rather than the much more complex approach Rails took internally. Is this approach consistent with how Rails has tackled the deprecation?

[sfnelson]

We also require activemodel. I think it's ok to assume Rails for this project and not add it to the gem spec.

[sfnelson]

Rails takes a similar but different approach that might be clearer: rails/rails@1719d25

class_attribute :config, instance_predicate: false, default: ActiveSupport::OrderedOptions.new

class_methods do
  def inherited(klass)
      klass.config = ActiveSupport::InheritableOptions.new(config)
      super
    end
end

[sobakasu]

ActiveSupport::InheritableOptions looks like it's designed to work with hashes, or OrderedOptions (which extends Hash). We are using Base::Config class for config. We could stick with .dup, or update config to use OrderedOptions (but then we'd be accepting any attribute rather than just paginate and sorting)

[sfnelson]

I meant the new approach, vs dup, and calling it before super