refactor: migrate package installation from pak to uvr

bincraft dropped pak in favour of uvr, so the pipelines, helper scripts
and images in this repo move with it.

- add local/uvr-install.sh as the single replacement for pak::pak(); it
  bootstraps a pinned uvr, mints a throwaway project under TMPDIR and
  runs `uvr add --no-install` + `uvr sync --library`, because `uvr add`
  refuses to run outside a project and only `sync` honours --library
- install bincraft via its Forgejo spec (forgejo::codefloe.com/rpkgs/
  bincraft@<tag>) instead of a git:: URL, keeping the git ls-remote tag
  resolution
- pass UVR_R_BIN/UVR_TARGET_LIB from install-bincraft.R so the
  per-R-minor passes target their own R and library
- replace R_PKG_CACHE_DIR with UVR_CACHE_DIR/UVR_PACKAGES_DIR on the
  persistent volume, preserving the amd64-off/arm64-on split
- drop trim_pkgcache_metadata() and its test; uvr's cache does not grow
  the way pkgcache's _metadata dir did
- let uvr install system requirements from its vendored
  r-system-requirements rules, replacing pak::sysreqs_db_update()
- migrate the shiny app image, the alpine reprex and the CRAN loading
  test; ship uvr-install.sh in the build-one image
- track the uvr pin with renovate

build-all-versions-install-deps.yaml

@@ -30,8 +30,9 @@
 #         from_secret: HETZNER_S3_SECRET_KEY_K3S
 #       # normal env vars
 #       GIT_USER: pat-s
-#       # set the location of the 'pkgcache' cache dir which persists the R package dependencies needed to install the packages themselves
-#       # R_PKG_CACHE_DIR: /mnt/cache/pkgcache
+#       # set the location of uvr's caches, which persist the R package dependencies needed to install the packages themselves
+#       # UVR_CACHE_DIR: /mnt/cache/uvr/cache
+#       # UVR_PACKAGES_DIR: /mnt/cache/uvr/packages
 #       R_LIBS_USER: /mnt/cache/R-pkgs
 #       CCACHE_DIR: /mnt/cache/ccache
 #     volumes:
@@ -39,9 +40,8 @@
 #     commands:
 #       - git clone -q https://pat-s:$$REPO_RO_TOKEN@git.devxy.io/devxy/build-cran-binaries.git .
 #       - mkdir -p /mnt/cache/R-pkgs
-#       - rm -rf /mnt/cache/R-pkgs/00LOCK-* /mnt/cache/R-pkgs/bincraft /mnt/cache/pkgcache
-#       - /opt/R/$R_VERSION/bin/R -q -e 'install.packages("pak", repos = sprintf("https://r-lib.github.io/p/pak/stable/%s/%s/%s", .Platform$pkgType, R.Version()$os, R.Version()$arch))'
-#       - /opt/R/$R_VERSION/bin/R -q -e 'pak::pak("git::https://codefloe.com/rpkgs/bincraft.git", dependencies = TRUE)'
+#       - rm -rf /mnt/cache/R-pkgs/00LOCK-* /mnt/cache/R-pkgs/bincraft /mnt/cache/uvr
+#       - UVR_R_BIN=/opt/R/$R_VERSION/bin/R local/uvr-install.sh forgejo::codefloe.com/rpkgs/bincraft
 #       - /opt/R/$R_VERSION/bin/R -q -e 'packageVersion("bincraft")'
 #       # - /opt/R/$R_VERSION/bin/R -q -e "future::plan('multisession', workers = 6L); pkgs = bincraft::query_packages_without_historic_versions('alpine322', 'amd64'); saveRDS(pkgs, '/mnt/cache/pkgs_amd64.rds')"
 #       - /opt/R/$R_VERSION/bin/R -q -e "future::plan('multisession', workers = 6L); pkgs = bincraft::query_packages_without_historic_versions('alpine323', 'arm64'); saveRDS(pkgs, '/mnt/cache/pkgs_arm64.rds')"