PostgreSQL compatibility: `extract(second ...)` should preserve fractional seconds

Split out from #22247.

### Mismatch

`extract(second ...)` should preserve fractional seconds.

```sql
SELECT extract(second from timestamp '2020-01-01 00:00:12.345678');
```

PostgreSQL:

```text
12.345678
```

DataFusion:

```text
12
```

### Expected behavior

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