Support correlated scalar subquery without aggregation

### Is your feature request related to a problem or challenge?

This is perfectly valid use of scalar subquery without aggregation.
This should work in DataFusion

```sql
WITH src AS (
SELECT *
FROM (VALUES
(1, NULL, 'Europe'),
(2, 1, 'Warsaw'),
(3, 1, 'Paris')
) t(id, parent_id, name)
)
SELECT
id,
name,
(SELECT p.name FROM src p WHERE p.id = s.parent_id) AS parent_name
FROM src s;
```

Currently this fails with

```
Invalid (non-executable) plan after Analyzer
caused by
Error during planning: Correlated scalar subquery must be aggregated to return at most one row
```

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

- https://github.com/apache/datafusion/issues/16134

Start by reproducing the SQL example from the issue and inspect the Analyzer error for correlated scalar subqueries. Trace the planning path that requires aggregation; done means the query executes successfully and returns each parent name without requiring aggregation, with coverage for the shown case.

Written by the indexing model from the issue text.