implement proper Event#inspect

The java event does not have an `inspect` method. it actually defaults to `to_s` which is not sufficient for debugging or error logging purposes.

```
@logger.error(:event => event)
```

should output more information that just the `to_s` representation of the event. The good news is that we get to correct the previous behaviour which actually ended in dumping the Event data multiple times because of the inner Accessors class referencing back into the Event.

relates to #4428