Support ':' as a sub-directory separator?

[kevinushey]

renv uses : in remote specifications, for indicating a sub-directory within a repository. For example:

renv::install("jashapiro/nestedpak:mypak")

This doesn't work with pak, as a final / is instead expected. Would it be possible for pak to support this notation as well?

For context, renv chose to use : here to avoid ambiguity with things like GitLab where repositories could be nested, so : allows us to disambiguate whether we're trying to refer to a sub-repository as opposed to a folder within the repository.

Associated issue: rstudio/renv#2011