Request: vertical-rtl

Thank you for the incredible piece of work. It is revolutionary for many needs.

From inspecting the code it looks like this doesn't support vertical text. Could you please add vertical-rtl (Japanese)? Or give us guidance on how to add it? Much appreciated.

No files or tests are named in the issue. Start by inspecting the code paths responsible for text measurement and layout, then trace how existing right-to-left handling is implemented. Done requires a defined approach for Japanese vertical-rtl support or documented guidance for extending the library.

Written by the indexing model from the issue text.