Simplify integration test to use IOError instead of mocking HTTPx errors

Instead of trying to create complex mock HTTPX::ErrorResponse and
HTTPX::HTTPError objects (which require many internal stubs), simply
raise an IOError to simulate a connection failure.

StreamRequest catches any error during streaming and retries, so the
specific error type doesn't matter for testing the retry behavior.

This approach is much simpler and more maintainable.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: justin808

react_on_rails_pro/spec/react_on_rails_pro/request_spec.rb

@@ -245,25 +245,9 @@
             # This simulates a connection error after partial data is sent
             mock_streaming_response(render_full_url, 200) do |yielder|
               yielder.call("#{original_chunks[0]}\n")
-              # Simulate connection error mid-stream by creating a mock error response
-              # Create a minimal mock request object that satisfies the ErrorResponse constructor
-              mock_options = instance_double(
-                HTTPX::Options,
-                timeout: {},
-                debug_level: 0,
-                debug: false
-              )
-              mock_request = instance_double(
-                HTTPX::Request,
-                uri: URI(render_full_url),
-                response: nil,
-                options: mock_options
-              )
-              error_response = HTTPX::ErrorResponse.new(
-                mock_request,
-                StandardError.new("Connection closed")
-              )
-              raise HTTPX::HTTPError, error_response
+              # Simulate connection error mid-stream
+              # StreamRequest catches any error and retries, so we can use a simple error
+              raise IOError, "Connection closed"
             end
           else
             # Second attempt: complete all chunks successfully