Criterion micro-benchmark for the `zccache warm` cache-restore fan-out.
Run:
```bash
soldr cargo bench -p zccache-cli --bench warm_restore
```
Each entry is independent; restore order doesn't matter. CI cache restores
can be 1k–5k outputs, so the per-file syscall cost dominates wall-clock time.
Counts: 100 / 1000 / 5000.