Use CellCanvas with multiple tomograms

There are 2 aspects of this, one is easier than the other:

1) Train a model on multiple tomograms
2) Apply a model to multiple tomograms

(2) is kinda addressed by things like https://github.com/cellcanvas/cellcanvas/issues/9#issuecomment-1973339045

However, (1) has some design/UI challenges because we currently are fairly tightly linked to just working on 1 tomogram at a time. Flagging @kandarpksk @Janeece

Both were requested by David Agard

Start by reviewing the current single-tomogram workflow and the linked CellCanvas issue comment about applying a model to multiple tomograms. Clarify the UI and design requirements for both training on multiple tomograms and applying a model to them. Done means both requested workflows are supported without being limited to one tomogram at a time.

Written by the indexing model from the issue text.