ENH: Number formatting support for excel styles
- [x] closes #22027 
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Add number formatting support to the excel styles using a fake css entry. 

```css
number-format: 0%;
```

Added new tests, updated docs, and manually verified outputs using both excel output engines that support styling. 