[WER] Better error message for wer
Hi ! I don't think this would solve this issue.
Currently it looks like there's a bug that converts the list `["hello it's nice"]` to a string `'["hello it's nice"]'` since this is what the metric expects as input. The conversion is done before the data are passed to `_compute()`.

This is `Value("string").encode_example` that is called to do the conversion. Since `str()` encoding is too permissive we should consider raising an error if the example is not a string (even though it can be converted to string).  > called

Ah yeah you're right I just opened https://github.com/huggingface/datasets/pull/3460 to fix that. It now raises an error instead of computing the wrong WER Thank you - that should be good enough!
Currently we have the following problem when using the WER. When the input format to the WER metric is wrong, instead of throwing an error message a word-error-rate is computed which is incorrect. E.g. when doing the following: 


```python
from datasets import load_metric

wer = load_metric("wer")

target_str = ["hello this is nice", "hello the weather is bloomy"]
pred_str = [["hello it's nice"], ["hello it's the weather"]]

print("Wrong:", wer.compute(predictions=pred_str, references=target_str))
print("Correct", wer.compute(predictions=[x[0] for x in pred_str], references=target_str))
```
We get:
```
Wrong: 1.0
Correct 0.5555555555555556
```

meaning that we get a word-error rate for incorrectly passed input formats. We should raise an error here instead so that people don't spent hours fixing a model while it's their incorrect evaluation metric is the problem for a low WER.