parameters need post-update hooks

[hugary1995]

When we update model parameters, some intermediate tensors that depend on the updated parameters should be updated as well. So in theory, whenever the parameters are updated, those intermediate tensors should be recalculated.

However, we don't want to calculate the intermediate tensors in the forward operator itself, as that potentially repeats a fair of computation. Ideally, we want models to register post-update hooks for parameters.