Enters an infinite loop when messages are too long

MuKav tries to remove messages history in the middle until the prompt size is less than MAX_LENGTH: https://github.com/ASSERT-KTH/DET-Gen/blob/main/src/chatgpt.py#L131

We should add a check like this:
```
if len(messages) < 6:
raise Exception("Messages are too long!!")
```

@bardia-mhd

Start in src/chatgpt.py around line 131, where message history is removed while the prompt exceeds MAX_LENGTH. Check the loop's behavior when fewer than six messages remain, then add the requested failure condition. Done means oversized messages raise the specified exception instead of looping indefinitely.

Written by the indexing model from the issue text.