exponential_ few fixes (1) lambda > 0 (2) mkl kernel to continuous (3) better error log on dtype (#92891)
Exponential distribution is continuous. Fixes CPU MKL exponential implementation to exclude integer dtypes.
```python
import torch
dtypes = [torch.uint8, torch.int8, torch.int16, torch.int32, torch.int64]
for dtype in dtypes:
x = torch.empty(10000, dtype=dtype).exponential_() # should fail !
print("dtype: ", x.dtype, "sum: ", x.sum())
```
### Additional Context
Related to #92709. This issue propagates to OpInfo of exponential.
```
AssertionError: The supported dtypes for exponential on device type cpu are incorrect!
The following dtypes worked in forward but are not listed by the OpInfo: {torch.int64, torch.uint8, torch.int8, torch.int16, torch.int32}.
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/92891
Approved by: https://github.com/CaoE, https://github.com/jgong5, https://github.com/ngimel
