[optim] Make casting to match params a hook (#106725)
Moves the logic to casting state to match parameters into a hook so that users can choose to enable their hooks before or after the casting has happened.
With this, there is a little bit of redundancy of the id_map building and the check that the param groups are still aligned in length.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106725
Approved by: https://github.com/albanD
