R: use remotes::local_install instead of deprecated devtools::install_local

[minrk]

devtools::install_local doesn't work anymore due to missing dependency on remotes, and is deprecated since 2.5.0.

We are not using an independently pinned versions of devtools, despite indications in the code that we appear to intend to. I'm not sure if this loss of pinning is intentional, since I'm not an R expert.

I also don't know the possible implications of this change for repos with older versions. This is just the command the deprecation message pointed me to.

[minrk]

I found that we have two choices:

1. use pak::install_local() which seems to unavoidably leave cache and tmp files for us to cleanup by hand, but appears to be the recommended 'new way' to do it, or
2. use remotes::install_local() which seems lighter weight, and is the missing dependency for the deprecated devtools::local_install that has stopped working, and doesn't seem to leave extra files around.

[minrk]

huh, cleaning out the cache seems to result in the package not being available with pak, so I guess remotes is the simpler choice.

[minrk]

this (including #1528) fixes the R tests, #1529 fixes unit tests, with both I think we're all green again.