consume callback has an incorrect typing

**Environment Information**
- node-rdkafka version [e.g. 2.3.3]: 2.18.0

**Steps to Reproduce**

Use `.consume(callback)` from typescript. Type of "messages" in the callback is `Message[]` while the lib returns a single message. I have to force cast it to use it:
```
consumer.consume((err, msg) => {
const message = msg as unknown as RDKafka.Message;
```

The .consume variant with two parameters is alright

Start with the TypeScript typing for the `.consume(callback)` entry point and compare it with the two-parameter `.consume` variant. Verify that the callback's single returned message is typed as `Message`, while the two-parameter variant remains correct, and confirm the example no longer needs a forced cast.

Written by the indexing model from the issue text.