[BUG]: $inferInsert and InferInsertModel do not include nullable fields.

### Report hasn't been filed before.

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

### What version of `drizzle-orm` are you using?

0.40.1

### What version of `drizzle-kit` are you using?

0.30.5

### Other packages

_No response_

### Describe the Bug

When defining a schema, $inferInsert and InferInsertModel do not include/infer fields that are nullable.

For example:

`
export const bases = pgTable('bases', {
status: varchar().notNull(),
id: uuid().primaryKey().defaultRandom(),
name: varchar().notNull(),
description: text()
});
`

export type InsertBase = InferInsertModel;

In the above schema, description is not included in InsertBase. It will only be included if you make it notNull().