Dev: DB transactions after v4.3

We need to discuss:

- [x] Allow manual DB transactions even when `DBDebug` is true.
- #6917
- `DBDebug` will be deprecated in the future if possible.
- Perhaps this setting should not be eliminated.
- This setting is widely used and needs a long period of time before removing it.
- [ ] Add `resetTransStatus()` method ?
- #8767
- [ ] Model validation error and transaction. See https://forum.codeigniter.com/showthread.php?tid=84887&pid=403200#pid403200

See https://github.com/codeigniter4/CodeIgniter4/pull/6886#issuecomment-1325774111, https://github.com/codeigniter4/CodeIgniter4/pull/6886#issuecomment-1324182519