[FIX] pivot: ensure correct format status in menu

[dhrp-odoo]

Description:

Since PR #4657, users can define a custom format for pivot measures by selecting a cell with a measure value and applying a format.

However, the format menu's tick status incorrectly displayed "Automatic" even after applying a custom format. This was caused by the getCell method fetching the cell format, which does not account for pivot measure-specific formats.

This fix ensures the format menu reflects the correct status by properly handling pivot cell measure formats.

Task: 4373606

review checklist

• feature is organized in plugin, or UI components
• support of duplicate sheet (deep copy)
• in model/core: ranges are Range object, and can be adapted (adaptRanges)
• in model/UI: ranges are strings (to show the user)
• undo-able commands (uses this.history.update)
• multiuser-able commands (has inverse commands and transformations where needed)
• new/updated/removed commands are documented
• exportable in excel
• translations (_t("qmsdf %s", abc))
• unit tested
• clean commented code
• track breaking changes
• doc is rebuild (npm run doc)
• status is correct in Odoo

[robodoo]