[BUG]: drizzle-zod incorrect mapping of date columns to zod string

### Report hasn't been filed before.

- [x] I have verified that the bug I'm about to report hasn't been filed before.

### Other packages

drizzle-zod@0.8.2

### Describe the Bug

For column of type `date({ mode: 'string' })` drizzle-zod uses `z.string()`
But zod 4 has `z.iso.date` type which represents specifically string iso date: https://zod.dev/api?id=iso-dates which validates format `YYYY-MM-DD` which is format the column with `date({ mode: 'string' })` type will return.

Currently there is a test in drizzle-zod for this case which ensures `date({ mode: 'string' })` will become `z.string()`
https://github.com/drizzle-team/drizzle-orm/blob/main/drizzle-zod/tests/pg.test.ts#L416
https://github.com/drizzle-team/drizzle-orm/blob/main/drizzle-zod/tests/pg.test.ts#L464

Introducing of this will be a breaking change.
Do you think we can implement such behavior?

Would you be open for a PR for this change?