Docs: format sys.float_info properly (#108107)

- Normalise capitalisation and punctuation
- Use attribute markup for named tuple attributes
- Use :c:macro: markup for C macros
- Use a list for the 'rounds' attribute values
- Use list-table, for better .rst readability
- Remove one unneeded sys.float_info.dig link

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>