Update kubb to allow nullable enum

[pratishta]

Closes #321

Will squash before merging after initial review. Upgrading Kubb resulted in:

• Having to update Zod version from 3.22 to 3.23 due to allowing Zod string to validate date format
• Updating the schema type in the pipes to expect union type for the schema params (e.g. ZodObject<T> to ZodObject<T> | ZodOptional<ZodObject<T>>.
• Forcing MVT schema to return a string

[TangoYankee]

Investigating downstream effects

[TangoYankee]

@pratishta , I'm working on the validation and decode pipes. I'll create a branch off of this one and share my findings when they're ready.

EDIT: The branch- ty/decode-param

[TangoYankee]

Closing in favor of #326, which has the updated pipes