fix: Preserve nested Bun package keys (#14050)
Fixes #14048.
Prevent Bun lockfile pruning from retaining workspace mappings whose
workspaces are outside the pruned graph. Nested external packages under
retained workspace scopes are also excluded from promotion, preserving
Bun's original package-key hierarchy when an external package shares a
name with another workspace.
Adds the issue reproduction as a Bun v2 lockfile fixture covering Docker
pruning for both affected targets.
Co-authored-by: vercel-gh-bot-5[bot] <312521305+vercel-gh-bot-5[bot]@users.noreply.github.com>