feat: storage: Force exit GenerateSingleVanillaProof on cancelled context

[magik6k]

Related Issues

Proposed Changes

• Add some more logs to wdpost cycle logic
• Respect context in local GenerateSingleVanillaProof
  • before it could block forever if underlying storage reads blocked, e.g. with disconnected NFS, which would lead to the entire PoSt failing
  • Now we'll return context error, which should result in only the slow-to-read sectors being skipped; There will also be a big, detailed log message printed.

Additional Info

Checklist

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