[ao][sparsity] Implemented state_dict() and load_state_dict() functions (#79883)
The state_dict() of the DataScheduler contains all the class attributes of
the scheduler other than the data_sparsifier.
Remember to store and restore the state_dict() of the data_sparsifier along
with the scheduler
Test Plan:
```python test/test_ao_sparsity.py TestBaseDataScheduler```
Differential Revision: [D37358607](https://our.internmc.facebook.com/intern/diff/D37358607)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/79883
Approved by: https://github.com/HDCharles, https://github.com/z-a-f
