Perplexity dtype restriction too strict

[ZhaofengWu]

🐛 Bug

The perplexity metric requires the input dtype to be either fp32 or fp64, but this doesn't work with e.g. fp16, and users need to manually recast.

torchmetrics/src/torchmetrics/functional/text/perplexity.py

Line 21 in 894de4c

_TORCH_FLOAT_OR_DOUBLE = (torch.float32, torch.float64)

Expected behavior

The metric should accept other floating point dtypes.