* feat: enhance `store prune` to clean global virtual store
`pnpm store prune` will now clean the global virtual store
via a new project registry and mark-and-sweep garbage collection.
* test: add store prune test for transitive dependency preservation
* refactor: extract global virtual store pruning logic to a new file
* fix: improve symlink handling in global virtual store pruning
* fix: optimize removal of unreachable packages in global virtual store
* fix: refine project registry error handling
Throw `PnpmError` for inaccessible projects
and specifically clean up stale symlinks for `ENOENT` errors.
* test: create virtual store with install command
* refactor: standardize global virtual store directory structure
by placing unscoped packages under an `@` scope.
* test: update store prune tests to use `toContain` and `not.toContain` assertions`
* fix: linting issues
* Apply suggestions from code review
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
* fix: implemented CR suggestions
* fix: revert not needed change
* fix: use `is-subdir` to accurately determine if symlink targets
are within the global virtual store.
* revert: changes in package.json files
* test: add `--config.ci=false` to store prune tests
