[BUG]: Unnecessary parentheses in UNION ALL subqueries for CTE statements causing syntax errors

### 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

## Description
When using the `unionAll` method to build Common Table Expressions (CTEs), Drizzle ORM adds extra parentheses around each subquery, which can cause syntax errors in some cases.

## Steps to Reproduce
When creating a CTE using this pattern:

```typescript
const cte = qb.$with('name').as(
qb
.select()
.from(tableA)
.where(/* condition */)
.unionAll(
qb
.select()
.from(tableB)
.where(/* condition */)
)
);
```

## Generated SQL (with issue)
```sql
with "name" as (
(select columns from tableA where condition)
union all
(select columns from tableB where condition)
)
```

## Expected SQL
```sql
with "name" as (
select columns from tableA where condition
union all
select columns from tableB where condition
)
```

## Root Cause
In the Drizzle ORM source code, the `unionAll` method implementation automatically adds parentheses around each subquery. While this might be necessary for standalone UNION ALL queries, it's redundant when building CTE subqueries and can lead to syntax errors.

## Suggested Fix
Modify the `unionAll` method implementation to avoid adding extra parentheses in CTE contexts, or provide an option to control whether parentheses are added around subqueries.