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.

まず、示されている Express handler を使用して AWS Lambda 上で @codegenie/serverless-express 4.16.0 の失敗を再現し、その後、4.15.0 と 4.16.0 の応答処理を比較します。レポートにはリポジトリのファイルやテストパスが記載されていないため、関連する応答処理のエントリポイントを特定し、4.15.0 の動作している挙動を維持したまま、ee.on エラーなしでリクエストが完了することを検証してください。

索引モデルが issue の本文から書いたものです。