Improve error message in `sqllogictest` with `<slt:ignore>` marker

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

Follow up to https://github.com/apache/datafusion/pull/18857

With `` feature, if the actual and expected is not matched, we got error message like

```
2. query result mismatch:
[SQL] select * from generate_series(3);
[Diff] (-expected|+actual)
-
+ 0
1
- 3
+ 2
3
at /Users/yongting/Code/datafusion/datafusion/sqllogictest/test_files/slt_features.slt:84
```

The first diff is a false positive, and the second one is expected. It would be great to suppress the 1st diff.

Also, the error message rendering and the actual validation for `sqllogictest` seems to live in two different places, it would be better to combine them.

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Riproduci la discrepanza da datafusion/sqllogictest/test_files/slt_features.slt alla riga 84, quindi traccia le posizioni separate di validazione e rendering degli errori di sqllogictest menzionate nell’issue. La modifica completata dovrebbe sopprimere il diff falso positivo causato da continuando comunque a segnalare la discrepanza reale, con coverage per questo output.

Scritto dal modello di indicizzazione a partire dal testo della issue.