Add a `dtype` option for `load_from_checkpoint`

Nobody has claimed this yet.

### Description & Motivation

Hi,
It would be nice to have a `dtype` argument for `load_from_checkpoint` along with the very cool `map_location`. It would allow the user to set the `dtype` automatically via `load_from_checkpoint` without the manual need of doing `.to(dtype)`.

### Pitch

The fix is should be pretty straightforward. Currently we have:
```python
def load_from_checkpoint(
cls,
checkpoint_path: Union[_PATH, IO],
map_location: _MAP_LOCATION_TYPE = None,
hparams_file: Optional[_PATH] = None,
strict: Optional[bool] = None,
**kwargs: Any,
) -> Self:
...
```

It would just get one more argument:
```python
def load_from_checkpoint(
cls,
checkpoint_path: Union[_PATH, IO],
map_location: _MAP_LOCATION_TYPE = None,
type:torch.dtype=None,
hparams_file: Optional[_PATH] = None,
strict: Optional[bool] = None,
**kwargs: Any,
) -> Self:
...
```

Given this actually points to `_load_from_checkpoint` https://github.com/Lightning-AI/pytorch-lightning/blob/3d398240d2f62f2ad05e9eff557d2d5cb44f235c/src/lightning/pytorch/core/saving.py#L53

We can add our extra `dtype` argument here too and can easily change this line https://github.com/Lightning-AI/pytorch-lightning/blob/3d398240d2f62f2ad05e9eff557d2d5cb44f235c/src/lightning/pytorch/core/saving.py#L99

to
```python
return model.to(dtype).to(device)
```

Hope this is taken into consideration :)

@Borda @awaelchli @lantiga

### Alternatives

_No response_

### Additional context

_No response_

Start in src/lightning/pytorch/core/saving.py, especially load_from_checkpoint, _load_from_checkpoint, and the return path around the referenced lines. Trace how map_location and kwargs flow through checkpoint loading, then check the surrounding tests for expected loading behavior. Done means the public and internal loading paths accept dtype and loaded models honor it without breaking existing arguments.

Written by the indexing model from the issue text.