Napari GUI: Fix voxel size precision, font size, and rearrange widgets

[qin-yu]

1. Fix Napari UI: Add model widget only takes two decimal in resolution #226: Previously, the voxel size was limited to two decimal places, which usually allowed for 1 or 2 significant figures. It now has 5 decimal places, which should be accurate enough for most purposes.
2. Fix Napari UI: Widgets too wide yet don't have enough space for numbers to show #213: Previously, the sliders had a large label size that could not fully display the values. The font size has now been adjusted.
3. Improve the fix for Too many elements in extra-seg #218: The previous fix involved hiding all widgets and allowing users to choose one to display. Now, all widgets are shown at launch, and users can select one and hide the others.
4. Rearrange widgets: Historically, the proofreading tools and I/O were considered "Main." However, as Napari-based PlantSeg has evolved, the tabs need to be rearranged.