go/worker/storage/committee: Delay fetching chunk when no peers available

[martintomazic]

Hot loop caused the worker's checkpoint sync to become stuck:

{"caller":"checkpoint_sync.go:108","chunk":161,"err":"no peers given to service the request","level":"error","module":"worker/storage/committee","msg":"failed to fetch chunk from peers","runtime_id":"000000000000000000000000000000000000000000000000f80306c9858e7279","ts":"2026-04-06T15:12:28.315550177Z"}
....  repeat N times

Solution:

• Add backoff/timeout or per-chunk backoff as suggested.
  • Lets keep it simple for the start and only have simple delay.
• Fix defer in the for loop (resource leak).