Change state_required detections

[DanielePalombo]

Carmen::Country#subregions? returns true even if the subregions aren't states.
With this commit state_required variable will set true only when there is at least one nested state.

To update existing countries you can execute the following command on the console.

require 'carmen'

carmen_countries = Carmen::Country.all

Spree::Country.all.each do |country|
  next if carmen_countries.detect { |c| c.name == country.name }.subregions.any? { |c| c.subregions.detect { |r| r.type == 'state' } }
  
  country.update(states_required: false)
end

Ref #3803

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• I have followed Pull Request guidelines
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[kennyadsl]

I'm not sure to get this. How having states as subregions and subregion being required are connected. For example, in Italy we have provinces, which are not states and they are required in the address.

[waiting-for-dev]

Closing in favor of #3842 to properly define all the logic involved here.