Fix client disconnect test to properly simulate stream.closed?

The test "stops producing when client disconnects" was failing because
the .closed? stub always returned false, so producers never detected
the disconnect.

Changes:
- Add stream_closed flag that starts as false
- Set stream_closed = true when IOError is raised (2nd write)
- Update .closed? stub to return the stream_closed flag value
- Move IOError raise before adding chunk to written_chunks
  (so written_chunks.count == 1 as expected, not 2)

This properly simulates the real behavior where stream.closed? returns
true after a write error, allowing producers to detect disconnect and
stop producing.

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

Co-Authored-By: Claude <[email protected]>

Author: ihabadham

react_on_rails_pro/spec/dummy/spec/helpers/react_on_rails_pro_helper_spec.rb

@@ -521,12 +521,19 @@ def execute_stream_view_containing_react_components
 
         # Simulate client disconnect by making stream.write raise IOError
         call_count = 0
+        stream_closed = false
         allow(mocked_stream).to receive(:write) do |chunk|
           call_count += 1
+          if call_count == 2
+            stream_closed = true
+            raise IOError, "client disconnected"
+          end
           written_chunks << chunk
-          raise IOError, "client disconnected" if call_count == 2
         end
 
+        # Update the closed? stub to check the stream_closed flag
+        allow(mocked_stream).to receive(:closed?) { stream_closed }
+
         # Configure render_to_string to call stream_react_component
         allow(self).to receive(:render_to_string) do
           render_result = stream_react_component(component_name, props: props, **component_options)