Add progress bars for longer processing tasks

Model fitting, prediction, and painting in the embedding can be time consuming. Currently there is just a hack that changes UI elements to be yellow to indicate something is happening. We should use a proper progress bar like napari's or https://pyapp-kit.github.io/magicgui/generated_examples/progress_bars/progress_indeterminate/

Inspect the embedding code paths for model fitting, prediction, and painting, then compare the existing yellow UI-state hack with napari's or magicgui's indeterminate progress-bar example. Done means those longer operations use a proper progress indicator instead of only changing UI elements to yellow; the issue names no files or tests to run.

Written by the indexing model from the issue text.