Runtime module should be treated as normal module in code splitting

See [this](https://github.com/rolldown-rs/rolldown/blob/a153950a1b7ecb176d595c27888a7fd7408ed0ee/crates/rolldown/src/bundler/bundle/bundle.rs#L191-L199) for details.