* fix: slash menu unexpectedly overflows the screen
* fix: the style of no result doesn’t match the design
* fix: unexpected flashing effect on 2nd level menu item
* fix: can not back to last level through backspace
* feat: support columns block in editor
* feat: upgrade simple columns block
* fix: build error
* feat: add column width resizer
* fix: drag visual border
* fix: drag button position issue
* feat: add rule to check if the column is empty
* fix: flutter analyze
* feat: add document rules to delete the columns if its children are empty
* feat: support adding image in columns block
* feat: integrate block actions in columns block
* feat: support dragging to create a columns block
* feat: drag a block into an existing columns block
* feat: add delete columns and delete column rules
* feat: dragging the block to the left side of another block to create a columns block
* feat: support 2-4 columns block in slash menu
* chore: disable debug flag in columns block
* chore: update pubspec.yaml
* chore: update translations and icons
* fix: cloud integration test
* fix: integration test
