Adding more frequency options to `ProgressCB`

I found it helpful to optionally change the `update_freq` of `ProgressCB` to be every epoch instead of every batch.

To me, there is no reason to update every batch when I can just do it every epoch and look at it after couple epochs to see how it was going.

Another helpful option is only show it after fit. When I am training for more than 10 epochs, I usually want to just look at it after it finished running. For me personally, I show first and second epochs, then don't update until it's done fitting.

I can add this if the community also finds it helpful.

The issue names ProgressCB, update_freq, epochs, batches, and fit, but no files or tests. Start by locating ProgressCB and reading how update_freq is handled during training; done means supporting epoch-only and post-fit display modes with behavior matching the requested training workflow.

Written by the indexing model from the issue text.