Simplified SAM segmentation in TIAViz

[measty]

This PR takes the sam-viz PR and fixes and substantially simplifies it.

I think the original PR was going for a more general prompt segmentor engine that would in theory cope with prompts dispersed over a whole WSI, but I think that approach has issues in practice (and it would also need some significant work to fix from its current state, I think). This PR focusses on segmenting prompts made within a specific view window, which I think is more practical and allows for a much simplified approach.

I'm adding this as a separate PR so we can discuss what approach to take and both PRs are available to look at.

Examples: