Add OpenDocument Spreadsheet (.ods) import/export support

[code-by-sia]

Summary

The roadmap marks Open Office format support as not implemented.

Scope

Support importing and exporting OpenDocument Spreadsheet files (.ods).

Acceptance criteria

• Open existing .ods files.
• Preserve cell values, formulas, merged cells and basic formatting where possible.
• Export current sheets to .ods.
• Gracefully handle unsupported features.
• Add interoperability tests using sample ODS documents.

Source

* [x] import/export
  * [ ] Open office format support