Further rendering improvements

[chrisvxd]

Further identified rendering improvements

Re-renders

1. Changing parent props (like root) causes all children to re-render
2. Hovering on outline causes re-render of all items
3. Siblings re-rendering during drag operation

Tasks

• Memoize DropZoneChild components to prevent re-rendering during reorder
• Don’t pass preview in as prop to DropZoneChild as this causes prop change and further re-renders. Instead, try zone context store.
• If possible don’t pass index in as prop into DropZoneChild as this is causing re-renders on duplicate for higher items (needed because of dndkit index). May require use of zone index after slots in Add slots API #984.
• DropZoneProvider causing various re-renders (and along with a lack of memoizing, is likely responsible for issue (1) and (2))
• Address other possible issues with existing zustand store implementation in DropZoneEdit (which may be nullified by above changes)
  • Hover
    • Move isDeepestZone to sibling, unless DropZone is empty
    • Refactor inNextDeepestZone class application to use :has
  • Drag start
    • useContentWithPreview refers to draggedItem, which means it will render the entire dropzone on drag start

Closes #644