Custom RuboCop to check `unscoped` positioning

gistfile1.txt

RuboCop:
```
# lib/rubocop/cop/style

# frozen_string_literal: true

module RuboCop
  module Cop
    module Style
      # `Client.unscoped.where(...)` is better than `Client.where(...).unscoped`
      #
      # @example
      #   # bad
      #   Client.where(...).unscoped
      #
      #   # good
      #   Client.unscoped.where(...)
      #
      class UnscopedPositioning < Base
        MSG = 'Use `.unscoped` immediately after the model name.'

        # We only care about method calls to `unscoped`
        RESTRICT_ON_SEND = %i[unscoped].freeze

        def on_send(node)
          return unless node.method?(:unscoped)

          receiver = node.receiver
          return unless receiver&.send_type?

          # Get the full chain of calls
          chain = build_method_chain(node)

          # We're only interested if `unscoped` is not the first call after the model
          # i.e., the model name should be the base of the chain, and `unscoped` should be next
          return unless chain.size > 1 && chain[0]&.const_type? && chain[1]&.method_name != :unscoped

          add_offense(node)
        end

        private

        # Builds an array of nodes representing the method chain
        # For `Client.where(...).order(...).unscoped`, returns:
        #   [Client, where, order, unscoped]
        def build_method_chain(node)
          chain = []
          while node
            chain.unshift(node)
            node = node.receiver if node.respond_to?(:receiver)
          end
          chain
        end
      end
    end
  end
end
```
RSepc:
```
# spec/rubocop/cop/style

# frozen_string_literal: true

require 'rubocop'
require 'rubocop/rspec/support'
require_relative '../../../../lib/rubocop/cop/style/unscoped_positioning'

RSpec.describe RuboCop::Cop::Style::UnscopedPositioning, :rubocop do
  subject(:cop) { described_class.new }

  context 'when unscoped comes after another query method' do
    it 'registers an offense for .where followed by .unscoped' do
      expect_offense(<<~RUBY)
        Client.where(status: :active).unscoped
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Style/UnscopedPositioning: Use `.unscoped` immediately after the model name.
      RUBY
    end

    it 'registers an offense for .joins followed by .unscoped' do
      expect_offense(<<~RUBY)
        Client.joins(:posts).unscoped
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Style/UnscopedPositioning: Use `.unscoped` immediately after the model name.
      RUBY
    end
  end

  context 'when unscoped is the first method call on the model' do
    it 'does not register an offense' do
      expect_no_offenses(<<~RUBY)
        Client.unscoped.where(status: :active)
      RUBY
    end

    it 'does not register an offense for complex chain starting with unscoped' do
      expect_no_offenses(<<~RUBY)
        Client.unscoped.joins(:posts).where(status: :active)
      RUBY
    end
  end

  context 'when no unscoped is used' do
    it 'does not register an offense' do
      expect_no_offenses(<<~RUBY)
        Client.where(status: :active)
      RUBY
    end
  end
end
```