improve max length handling

### Bug description

Currently, the algorithm in `textsplit.py` will cut a sentence off at the `max_length`, even if this splits up a word. Instead, this algorithm should **always** preserve words and perhaps even preserve whole sentences or phrases.

### How to reproduce the bug

```python
# Sample code to reproduce the problem
```

### Error messages and logs

```
# Error messages and logs here please
```

### Environment

Current environment

# Please paste the output of `everyvoice --diagnostic` here

# EveryVoice Diagnostic information

### More info

_No response_