Add RSpec matchers for turbo stream and turbo frames

[bastin27]

Summary

• Add have_turbo_stream matcher to assert <turbo-stream> elements by action and target/targets, with optional .with_count(n) chaining
• Add be_turbo_stream matcher to verify Turbo Stream content type (text/vnd.turbo-stream.html)
• Add have_turbo_frame matcher to assert <turbo-frame> elements by id
• Add has_turbo? feature check for conditional loading when turbo-rails is available
• Update scaffold generator to include turbo_stream format tests for create, update, and destroy actions
• CSS selector values are escaped to prevent selector injection in Nokogiri queries
• Includes Cucumber feature specs and RSpec unit tests (36 examples)

Test plan

• All 36 turbo matcher specs pass
• Verify Cucumber feature specs pass with turbo-rails available
• Test scaffold generator output includes turbo_stream format tests
• Confirm matchers work in a real Rails 7+ app with Turbo enabled

Related issue: #2887

[JonRowe]

👋 Sorry for the delay in looking at this, its something thats worth having but I feel prehaps that instead we should be leveraging the Rails assertations using:

match_unless_raises ActiveSupport::TestCase::Assertion do
  @scope.assert_... 
end

Style checks rather than re-building them in matchers...

[JonRowe]

As above, you should be able to call this already

[JonRowe]

This should be available already

[JonRowe]

These should be wrapped in an if statement that only emits the fragment if Turbo is enabled e.g. (note the -%> which remove the if line whitespace from the output)

Suggested change

	context "with turbo_stream format", if: defined?(Turbo) do
	it "creates a new <%= class_name %> and responds with turbo stream" do
	post <%= index_helper %>_url, params: { <%= singular_table_name %>: valid_attributes }, as: :turbo_stream
	expect(response).to be_turbo_stream
	end
	end
	<% if RSpec::Rails::FeatureCheck.has_turbo? -%>
	context "with turbo_stream format" do
	it "creates a new <%= class_name %> and responds with turbo stream" do
	post <%= index_helper %>_url, params: { <%= singular_table_name %>: valid_attributes }, as: :turbo_stream
	expect(response).to be_turbo_stream
	end
	end
	<% end -%>