Turbopack: flush Node.js worker IPC on error (#84077)
If the Nodejs process exited too quickly after `sendError`, Turbopack never received the error message and then previously crashed with panics such as
```
- Execution of PostCssTransformedAsset::process failed
- creating new process
- reading packet length
- unexpected end of file
```
Now, flush the socket before calling `process.exit()`
