PostgreSQL compatibility: `round(float8)` should match PostgreSQL half-tie behavior

Split out from #22247.

### Mismatch

`round(float8)` should match PostgreSQL half-tie behavior (banker's rounding / round-half-to-even).

```sql
SELECT round(2.5::float8);
```

PostgreSQL:

```text
2
```

DataFusion:

```text
3.0
```

### Expected behavior

For PostgreSQL-compatible SQL semantics, DataFusion should either match PostgreSQL's result or raise the same class of domain/semantic error.