Roxygenize rgrass documentation

[stevenpawley]

Purpose

This is a pull request to roxygenize the rgrass documentation. This should reproduce the original documentation but using roxygen2 tags. The code examples within the documentation have been reformatted for readability, although there are no logic changes to the examples.

Testing

Examples have been checked in the GRASS NC basic dataset. Documentation and package build passes devtools::check() with:

0 errors ✔ | 0 warnings ✔ | 0 notes ✔

Note

Note, the read_RAST example that returns data using 'sp' fails due to the PROJ4 string from GRASS (using GRASS 8.3.2 on Ubuntu 24.04).

[stevenpawley]

Thanks for reviewing this!