Update tests to use ProUtils for immediate_hydration

Changes test setup to stub ReactOnRails::ProUtils.immediate_hydration_config
instead of setting config.immediate_hydration on ReactOnRails configuration.
This aligns with the new architecture where immediate_hydration is a Pro-only
configuration option.

Also removes config.immediate_hydration from the dummy app initializer as it
is no longer a valid ReactOnRails configuration option.

Author: claude

spec/dummy/config/initializers/react_on_rails.rb

@@ -41,6 +41,5 @@ def self.adjust_props_for_client_side_hydration(component_name, props)
   config.rendering_props_extension = RenderingPropsExtension
   config.components_subdirectory = "startup"
   config.auto_load_bundle = true
-  config.immediate_hydration = false
   config.generated_component_packs_loading_strategy = :defer
 end

spec/dummy/spec/helpers/react_on_rails_helper_spec.rb

@@ -38,15 +38,8 @@ def self.pro_attribution_comment
     stub_const("ReactOnRailsPro", pro_module)
     stub_const("ReactOnRailsPro::Utils", utils_module)
 
-    # Configure immediate_hydration to true for tests since they expect that behavior
-    ReactOnRails.configure do |config|
-      config.immediate_hydration = true
-    end
-  end
-
-  after do
-    # Reset to default - avoid validation issues by setting directly
-    ReactOnRails.configuration.immediate_hydration = false
+    # Stub immediate_hydration to true for tests since they expect that behavior
+    allow(ReactOnRails::ProUtils).to receive(:immediate_hydration_config).and_return(true)
   end
 
   let(:hash) do

spec/dummy/spec/system/integration_spec.rb

@@ -104,12 +104,9 @@ def self.pro_attribution_comment
     end
     stub_const("ReactOnRailsPro", pro_module)
     stub_const("ReactOnRailsPro::Utils", utils_module)
-  end
 
-  around do |example|
-    ReactOnRails.configure { |config| config.immediate_hydration = true }
-    example.run
-    ReactOnRails.configure { |config| config.immediate_hydration = false }
+    # Stub immediate_hydration to true since these tests expect that behavior
+    allow(ReactOnRails::ProUtils).to receive(:immediate_hydration_config).and_return(true)
   end
 end