Encapsulate stale_when_importmap_changes method #556

Job	Run time
Tests (Ruby 3.2, Gemfile)	1m 37s
Tests (Ruby 3.2, gemfiles/rails_7_0_propshaft.gemfile)	45s
Tests (Ruby 3.2, gemfiles/rails_7_1_propshaft.gemfile)	56s
Tests (Ruby 3.2, gemfiles/rails_7_2_propshaft.gemfile)	58s
Tests (Ruby 3.2, gemfiles/rails_main_propshaft.gemfile)	1m 4s
Tests (Ruby 3.2, gemfiles/rails_7_0_sprockets.gemfile)	49s
Tests (Ruby 3.2, gemfiles/rails_7_1_sprockets.gemfile)	53s
Tests (Ruby 3.2, gemfiles/rails_7_2_sprockets.gemfile)	57s
Tests (Ruby 3.2, gemfiles/rails_main_sprockets.gemfile)	57s
Tests (Ruby 3.3, Gemfile)	1m 34s
Tests (Ruby 3.3, gemfiles/rails_7_0_propshaft.gemfile)	49s
Tests (Ruby 3.3, gemfiles/rails_7_1_propshaft.gemfile)	58s
Tests (Ruby 3.3, gemfiles/rails_7_2_propshaft.gemfile)	1m 0s
Tests (Ruby 3.3, gemfiles/rails_main_propshaft.gemfile)	1m 1s
Tests (Ruby 3.3, gemfiles/rails_7_0_sprockets.gemfile)	51s
Tests (Ruby 3.3, gemfiles/rails_7_1_sprockets.gemfile)	59s
Tests (Ruby 3.3, gemfiles/rails_7_2_sprockets.gemfile)	1m 0s
Tests (Ruby 3.3, gemfiles/rails_main_sprockets.gemfile)	1m 0s
Tests (Ruby 3.1, gemfiles/rails_7_0_propshaft.gemfile)	53s
Tests (Ruby 3.1, gemfiles/rails_7_1_propshaft.gemfile)	54s
Tests (Ruby 3.1, gemfiles/rails_7_0_sprockets.gemfile)	47s
Tests (Ruby 3.1, gemfiles/rails_7_1_sprockets.gemfile)	57s
	21m 39s

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