fix: add cancellation handling in proving

[th7nder]

Description

While testing I couldn't kill the storage provider cause it was indifferent to my requests.
I added cancellation token handling where it made sense.

Number(1) }))
2024-12-13T15:33:39.759387Z  INFO prove_commit{sector_number=SectorNumber(1)}: polka_storage_provider_server::pipeline: Starting prove commit
2024-12-13T15:33:39.759945Z  INFO prove_commit{sector_number=SectorNumber(1)}: polka_storage_provider_server::pipeline: Wait for block 52 to get randomness
^C2024-12-13T15:33:47.951085Z  INFO polka_storage_provider_server: SIGTERM received, shutting down...
2024-12-13T15:33:47.951133Z  INFO polka_storage_provider_server: sent shutdown signal
2024-12-13T15:33:47.951183Z  WARN polka_storage_provider_server::pipeline: submit_windowed_post for deadline 0 has been cancelled.
2024-12-13T15:33:47.951211Z  WARN polka_storage_provider_server::pipeline: submit_windowed_post for deadline 2 has been cancelled.
2024-12-13T15:33:47.951229Z  INFO start_pipeline: polka_storage_provider_server::pipeline: Pipeline has been stopped by the cancellation token...
2024-12-13T15:33:47.951238Z  WARN polka_storage_provider_server::pipeline: submit_windowed_post for deadline 1 has been cancelled.
2024-12-13T15:33:47.951314Z  WARN prove_commit{sector_number=SectorNumber(1)}: polka_storage_provider_server::pipeline: Cancelled while waiting to get randomness at block 52
2024-12-13T15:33:47.951358Z ERROR polka_storage_provider_server::pipeline: Failed ProveCommit for Sector: 1 err=Proving cancelled
[1]    88694 terminated  examples/start_sp.sh examples/test-data-big.txt

Checklist

• Are there important points that reviewers should know?
  • If yes, which ones?
• Make sure that you described what this change does.
• Have you tested this solution?

[jmg-duarte]

Looks ok to me