fix: Fall back to networked lockfile sync when pruning with cold caches
Validated Cargo prune against the Next.js/Turbopack workspace (65 crates,
1,140 lock packages, git-patched crates.io deps, nested member globs).
The offline lockfile canonicalization fails on machines that have never
built the repo: git-patch sources aren't in Cargo's cache, so `cargo
metadata --offline` cannot resolve. Retry without `--offline` before
degrading to the superset-lock warning.
With the fallback, pruning turbopack-cli emits a fully canonicalized
845-package lock that passes `cargo metadata --locked` immediately, and a
pruned send-trace-to-jaeger workspace compiles with `cargo build --locked`.