Bug Report: ee.on is not a function Error with @codegenie/serverless-express 4.16.0

### __Environment:__

- __@codegenie/serverless-express:__ 4.16.0 (error occurs) / 4.15.0 (works)
- __Express:__ 4.19.2
- __Node.js:__ 20.x (AWS Lambda runtime)
- __TypeScript:__ 5.7.3

### __Error Description:__

When using @codegenie/serverless-express version 4.16.0, the following error occurs consistently in AWS Lambda:

```javascript
TypeError: ee.on is not a function
at first (/var/task/node_modules/ee-first/index.js:43:10)
at onSocket (/var/task/node_modules/on-finished/index.js:115:16)
at attachFinishedListener (/var/task/node_modules/on-finished/index.js:120:5)
at attachListener (/var/task/node_modules/on-finished/index.js:147:5)
at onFinished (/var/task/node_modules/on-finished/index.js:53:3)
at send (/var/task/node_modules/finalhandler/index.js:314:3)
at /var/task/node_modules/finalhandler/index.js:133:5
at /var/task/node_modules/express/lib/router/index.js:646:15
at next (/var/task/node_modules/express/lib/router/index.js:265:14)
at urlencodedParser (/var/task/node_modules/body-parser/lib/types/urlencoded.js:91:7)
```

### __Root Cause:__

The error appears to be introduced in version 4.16.0 of @codegenie/serverless-express. The `ee-first` library expects an EventEmitter-like object but receives something that doesn't have the `.on()` method, suggesting a regression in how response objects are handled in the Lambda environment.

### __Reproduction Steps:__

1. Create a Lambda function with @codegenie/serverless-express 4.16.0
2. Set up basic Express routes
3. Deploy to AWS Lambda
4. Make any HTTP request to the Lambda function

### __Workaround/Solution:__

Downgrade to the previous working version:

```json
{
"@codegenie/serverless-express": "^4.15.0"
}
```

### __Code Pattern That Triggers Error:__

```typescript
import express from 'express';
import serverlessExpress from '@codegenie/serverless-express';

const app = express();
app.get('/health', (req, res) => res.send('ok'));

// This pattern causes the error with version 4.16.0
const serverlessHandler = serverlessExpress({ app });

export const handler = async (event, context) => {
return serverlessHandler(event, context, () => {});
};
```

### __Expected Behavior:__

The serverless handler should process requests without throwing `ee.on is not a function` errors.

### __Actual Behavior:__

The error occurs during response processing, specifically when Express tries to attach event listeners for response completion tracking.

### __Additional Context:__

- The error only occurs in AWS Lambda environment, not in local development
- The error happens after successful initialization but during request processing
- Downgrading to 4.15.0 completely resolves the issue
- This suggests a regression introduced in version 4.16.0

### __Version Comparison:__

- __4.15.0:__ ✅ Works correctly
- __4.16.0:__ ❌ Throws `ee.on is not a function` error

### __Suggested Investigation:__

Please review changes made between versions 4.15.0 and 4.16.0, particularly around response object handling and event emitter interactions in the Lambda environment.

Bắt đầu bằng cách tái hiện lỗi với @codegenie/serverless-express 4.16.0 trên AWS Lambda bằng Express handler được cung cấp, sau đó so sánh cách xử lý response giữa 4.15.0 và 4.16.0. Báo cáo không nêu file nào trong repository hoặc test path nào, vì vậy hãy xác định entry point liên quan đến việc xử lý response và xác minh rằng các request hoàn tất mà không có lỗi ee.on, đồng thời giữ nguyên hành vi đang hoạt động của 4.15.0.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.