Intertwine computation of metrics and tiff output in callbacks

[jonasteuwen]

Is your feature request related to a problem? Please describe.
Currently there is no way to delete h5s before the end of the epoch while these can be huge. Since they are used downstream in the tiffwriter and wsimetrics they are currently required.

Describe the solution you'd like
Compute metrics and write tiffs as soon as one is available and do not wait until it’s all done.

Describe alternatives you've considered
As is, but the h5s become large

Additional context
N/A