add forward declaration in stateful dataset (#22562)
Summary:
Addressing potential dependency issue by adding forward declaration for OutputArchive/InputArchive.
This change follows the same pattern in base.h in 'torch/csrc/api/include/torch/data/samplers/base.h'
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22562
Differential Revision: D16161524
Pulled By: soumith
fbshipit-source-id: d03f8a2ece5629762f9fa8a27b15b0d037e8f07b
