Update spatial cheatsheet links to point to rdrr

When we initialized the spatial training module cheatsheet, many of the bioc packages (VisiumIO, SpotSweeper, and ggspavis) hadn't yet made it to rdrr. For now, we are linking vignettes and similar for these functions. This may come up with additional packages as we continue developing these materials.

This issue tracks revisiting the cheatsheet down the line to see if we can update links to rdrr for overall consistency. But, this is minor in the scheme of things because the links we are currently providing get the job done just as well.

Open the spatial training module cheatsheet and review its links for the Bioconductor packages mentioned in the issue, including VisiumIO, SpotSweeper, and ggspavis. Replace available vignette or similar links with rdrr links for consistency, while retaining working alternatives for packages that are not available there.

Written by the indexing model from the issue text.