Update Zod Compatibility to Zod 4 instead of 3.

[nova4lb]

Confirm this is a feature request for the Node library and not the underlying OpenAI API.

• This is a feature request for the Node library

Describe the feature or improvement you're requesting

The library does not work with Zod 4 and should be updated

Additional context

No response

[namchuai]

#1612