Precision being changed from float16 to float32 unexpectedly
This is because of the formatter (`torch` in this case).
It defaults to `float32`.

You can load it in `float16` using `dataset.set_format("torch", dtype=torch.float16)`. I am having a similar issue when _building_ a dataset given `float16`-valued data.

```py
from datasets import Features, Value, Dataset

d = Dataset.from_dict({"data": np.ones(4, dtype="float16")}, features=Features({"data": Value("float16")}))
type(d["data"][0])  # returns <class 'float'>
```

Note that I specifically indicate that my data is `float16`-valued in the `features` argument above
### Describe the bug

I'm loading a HuggingFace Dataset for images. 

I'm running a preprocessing (map operation) step that runs a few operations, one of them being conversion to float16.  The Dataset features also say that the 'img' is of type float16.  Whenever I take an image from that HuggingFace Dataset instance, the type turns out to be float32.  



### Steps to reproduce the bug

```python
import torchvision.transforms.v2 as transforms
from datasets import load_dataset

dataset = load_dataset('cifar10', split='test')
dataset = dataset.with_format("torch")

data_transform = transforms.Compose([transforms.Resize((32, 32)), 
                                     transforms.ToDtype(torch.float16, scale=True),
                                     transforms.Normalize([0.5, 0.5, 0.5], [0.5, 0.5, 0.5]),
                                     ])
def _preprocess(examples):
    # Permutes from (BS x H x W x C) to (BS x C x H x W)
    images = torch.permute(examples['img'], (0, 3, 2, 1))
    examples['img'] = data_transform(images)
    return examples

dataset = dataset.map(_preprocess, batched=True, batch_size=8)
```

Now at this point the dataset.features are showing float16 which is great because that's what I want. 

```python
print(data_loader.features['img'])

Sequence(feature=Sequence(feature=Sequence(feature=Value(dtype='float16', id=None), length=-1, id=None), length=-1, id=None), length=-1, id=None)
```

But when I try to sample an image from this dataloader; I'm getting a float32 image, when I'm expecting float16:
```python
print(next(iter(data_loader))['img'].dtype)

torch.float32
```

### Expected behavior

I'm expecting the images loaded after the transformation to stay in float16.

### Environment info

- `datasets` version: 2.18.0
- Platform: Linux-5.15.146.1-microsoft-standard-WSL2-x86_64-with-glibc2.31
- Python version: 3.10.9
- `huggingface_hub` version: 0.21.4
- PyArrow version: 14.0.2
- Pandas version: 2.0.3
- `fsspec` version: 2023.10.0