Use pkgdepends for package installation

[hongooi73]

https://github.com/r-lib/pak
https://cran.r-project.org/package=pak

Among other things, should be much better than screen-scraping to detect install results.

EDIT: pak is the frontend, pkgdepends is the backend, yet to be submitted to CRAN

[hongooi73]

pkgdepends/pkgcache by default caches the latest versions of packages it's seen, which is NOT what we want for checkpointing purposes.

[hongooi73]

pkgdepends/pkgcache by default caches the latest versions of packages it's seen, which is NOT what we want for checkpointing purposes.

Actually because ~/.Rprofile is being read: r-lib/pkgdepends#168

[hongooi73]

Solved using withr::with_options().

[hongooi73]

Local MRAN will require pkgdepends support: r-lib/pkgdepends#88