feat: add support for nested identifiers for reference images

Vips will soon be introduced with its own set of expected render outputs for the same operations, so some mechanism for
scoping reference images is needed

spec/morandi_spec.rb

@@ -45,7 +45,10 @@
     FileUtils.remove_dir('sample/')
   end
 
-  shared_examples 'an image processor' do
+  shared_examples 'an image processor' do |processor_name|
+    let(:reference_image_prefix) { processor_name == 'pixbuf' ? '' : processor_name }
+    subject(:process_image) { Morandi.process(file_arg, options, file_out, { 'processor' => processor_name }) }
+
     describe 'when given an input without any options' do
       it 'creates output' do
         process_image
@@ -487,7 +490,7 @@
   end
 
   context 'pixbuf processor' do
-    it_behaves_like 'an image processor'
+    it_behaves_like 'an image processor', 'pixbuf'
 
     describe 'when given a pixbuf as an input' do
       subject(:process_image) do

spec/support/match_reference_image.rb

@@ -72,8 +72,9 @@ def expose_from(file_type:, tested_path: nil, reference_path: nil, diff_path: ni
   end
 end
 
-RSpec::Matchers.define :match_reference_image do |reference_name, file_type: 'jpg', tolerance: 0|
-  reference_path = File.join('spec/fixtures/reference_images', "#{reference_name}.#{file_type}")
+RSpec::Matchers.define :match_reference_image do |*reference_id, file_type: 'jpg', tolerance: 0|
+  *reference_scope, reference_name = reference_id
+  reference_path = File.join('spec/fixtures/reference_images', *reference_scope, "#{reference_name}.#{file_type}")
 
   def debug_data
     metadata = RSpec.current_example.metadata