Dataclass renderring is a bit ugly

[NicolasHug]

The way dataclasses are rendered is long and not super compact:

This has to do with the template that we're using:

https://github.com/pytorch-labs/torchcodec/blob/ffda77a1311b04022bfb904c55749e6a2d6ce67f/docs/source/api_ref_decoders.rst?plain=1#L22

There are probably different ways this can be tweaked. If we remove the template, the default rendering is more compact:

but it comes with other issues like the __init__ being displayed twice. And the docstring of each attribute is truncated after the first ., which isn't good.