feat: add support for multiple columns

#321Pull Requestlars250698 创建于 2024-11-30

### Changes Introduced - slides can now be split into multiple columns using `-|-` - VirtualText is displayed below the columns ![Screenshot 2024-11-29 at 12 07 38](https://github.com/user-attachments/assets/086d205c-1858-486e-85f8-02ea8efdff65) ![Screenshot 2024-11-29 at 12 07 47](https://github.com/user-attachments/assets/200c43db-0c49-47fb-aa05-786298e909ca) ![Screenshot 2024-11-29 at 12 07 55](https://github.com/user-attachments/assets/1034e764-8181-4909-86d2-8b859447146e)

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