Simplify default styling

[JulienBlasco]

I find the default styling a little bit confusing:

• columns are very wide
• only two footnotes are in bold

How about simplifying that a bit @ddotta?

The default bold font for title and header looks OK to me though.

[ddotta]

@JulienBlasco Yes, I'm not against simplifying the default stylization of tables.

I'm open to style suggestions 😄 (it's true that the columns are too wide).

For the future, maybe we could even consider tablexslx proposing style templates?
For example, to create Excel workbooks with the French state charter? See: https://github.com/spyrales/gouvdown?tab=readme-ov-file
(well, for the moment I don't see anything specific related to tables...)