Design CSV viewer mode with spreadsheet UI

lets revuew @docs/EDITOR_UI_REFERENCE.md and the codebase, and lets sketch out a feature design document for a dedicated "CSV viewer" mode for .csv files that will show the rows/cols as a spreadsheet, similar to how tableplus works for databases etc, use librarian to look at how https://github.com/Tablecruncher/tablecruncher is implemented and lets adapt that to work in rust for our csv viewer, it should integrate neatly into our existing codebase and is only relevant for tabular data (csv, tsv, etc), we would need a command to toggle it on/off for the current editor/file and should be able to handle failures (not a csv file, unparsable csv file, etc) and show this as a statusbar message using the existing mechanisms, we need tests for this feature inparticular, we can use a crate for csv parsing , should allow editing of indiviudual cell values while in this mode, and be able to sync the text/csv view when changes are made, should include a benchmark/stress test to ensure we can handle at least 1k,5k, 50k, 500k long csv files (generate them dynamically), and should handle scrolling horizontally when there are too many columns to comfortably fit in view at once, every part of this behaviour must be well documented and specified, data models and how to render it efficiently, sync state and cell values on edit etc, place it in docs/features/csv-editor.md it is fine to split this feature into multiple phases (start with readonly, then add editing support, then incrementally add features etc).