fix: Re-export magrittr pipe from magrittr

[gadenbuie]

The tidyverse is moving away from using or re-exporting the magrittr pipe and currently gtExtras is getting the pipe from dplyr. I wasn't able to reproduce locally, but on CI with ubuntu-24.04, gtExtras 0.6.2 wouldn't work with dplyr 1.2.1, routinely throwing

Error:
  ! package or namespace load failed for 'gtExtras' in get(n, ns):
   object '%>%' not found

This PR

• moves magrittr from Suggests to Imports
• imports and re-exports %>% from magrittr rather than dplyr
• cleans up a stray importFrom("gt", "%>%")

I also had to re-document, which meant bumping up to use the latest roxygen2. Oh, and bumping the gtExtras package version to 0.6.2.9000.