Support Workbook.AutosaveOn = False for the duration of an Excel.run call

The Velixo add-in is heavy in bulk operations (like drill-down rendering or formula removal/replacement with static values) that require multiple context.sync() calls.

• Data integrity: Intermediate states during a long run might not be meaningful to persist. Disabling autosave ensures only the final, correct result is saved.
• Performance: Saving less frequently, especially when we know that "now is not yet the time to auto-save", improves performance.
• Transactionality: When running an Excel interop process with Velixo, we want to either fully complete a set of changes or roll back.
• Avoid persisting potentially sensitive temporary data – any temporary confidential data that occurs in the workbook during an Excel.run process should never be persisted.