Timeout prevents Node.JS from exiting

#### Environment details

- Programming language: Javascript
- OS: Windows
- Language runtime version: Node v20.3.1
- Package version: 1.1.0

#### Steps to reproduce

1. Construct a `vertexAI.getGenerativeModel` with a timeout specified in the requestOptions
2. Finish the node script.
3. https://github.com/googleapis/nodejs-vertexai/blob/2ec9e7d5519af438eb03b9f21f90b86f2575ac47/src/functions/post_request.ts#L97 prevents node from exiting until the timeout elapses

Expected behavior: I would like the ability to set a timeout but also exit node immediately without waiting for the timeout to elapse.