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

.crow/weekly-rebuild-missing.yaml

@@ -141,7 +141,8 @@ steps:
       FORGEJO_TOKEN:
         from_secret: FORGEJO_TOKEN
       GIT_USER: pat-s
-      R_PKG_CACHE_DIR: /mnt/cache/pkgcache
+      UVR_CACHE_DIR: /mnt/cache/uvr/cache
+      UVR_PACKAGES_DIR: /mnt/cache/uvr/packages
       R_LIBS_USER: /mnt/cache/R-pkgs
       R_VERSION: ${R_VERSION}
       CCACHE_DIR: /mnt/cache/ccache
@@ -150,12 +151,12 @@ steps:
       NCPUS: 2
     commands:
       - git clone -q https://pat-s:$$REPO_RO_TOKEN@git.devxy.io/devxy/build-cran-binaries.git .
-      - mkdir -p /mnt/cache/pkgcache /mnt/cache/R-pkgs /mnt/cache/ccache /mnt/cache/packages
+      - mkdir -p /mnt/cache/uvr/cache /mnt/cache/uvr/packages /mnt/cache/R-pkgs /mnt/cache/ccache /mnt/cache/packages
       - rm -rf /mnt/cache/R-pkgs/00LOCK-*
       - /opt/R/$R_VERSION/bin/Rscript local/install-bincraft.R
       - /opt/R/$R_VERSION/bin/R -q -e 'packageVersion("bincraft")'
       - XVFB=$(command -v xwfb-run 2>/dev/null || command -v xvfb-run); XVFB_ARGS=""; if command -v xwfb-run >/dev/null 2>&1; then dnf install -y -q weston 2>/dev/null; XVFB_ARGS="-c weston"; fi
-      - /opt/R/$R_VERSION/bin/R -q -e 'pak::pak("httr2")'
+      - UVR_R_BIN=/opt/R/$R_VERSION/bin/R local/uvr-install.sh httr2
       - /opt/R/$R_VERSION/bin/R -q -e 'source("local/fetch-rebuild-packages-from-issue.R")'
       - $XVFB $XVFB_ARGS -- /opt/R/$R_VERSION/bin/R -q -e "sink(stdout(), type = 'message'); options(crayon.enabled = TRUE, Ncpus = $NCPUS, future.globals.onReference = NULL); pkgs <- readLines('/tmp/rebuild_pkgs.txt'); if (length(pkgs) == 0) { cat('Nothing to rebuild\n'); q('no') }; excluded <- jsonlite::fromJSON('local/excluded-packages.json')[['package']]; pkgs <- setdiff(pkgs, excluded); cat(sprintf('Rebuilding %d packages\n', length(pkgs))); n <- length(pkgs); for (i in seq_along(pkgs)) { x <- pkgs[i]; cat(sprintf('[%d/%d] %s\n', i, n, x)); tryCatch(bincraft::build_binary_package(x, tag_limit = 1L, patches = 'local/patches', s3_endpoint = 'https://s3.eu-central-003.backblazeb2.com', s3_region = 'eu-central-003', s3_bucket = 'devxy-rpkgs-binaries', s3_access_key_id = Sys.getenv('B2_S3_ACCESS_KEY'), s3_secret_access_key = Sys.getenv('B2_S3_SECRET_KEY'), metadata_db_host = 'r-binaries.devxy.io', metadata_db_name = 'build_metadata', metadata_db_table = 'single_builds', metadata_db_user = 'rpkgs', metadata_db_password = Sys.getenv('PGPASS'), metadata_db_sslmode = 'require', metadata_db_port = 15432, archive = TRUE, upload = TRUE, store_build_metadata = TRUE), error = function(e) cat(sprintf('ERROR building %s - %s\n', x, conditionMessage(e)))) }" 2>&1
     backend_options: