Detect block building completion

[therustmonk]

📝 Summary

The channel was not used previously, and this change makes BlockPayloadJob aware of the completion of the building.

💡 Motivation and Context

ToDo

• Determine whether the job should remain active for some time after the assembly is complete.

✅ I have completed the following steps:

• Run make lint
• Run make test
• Added tests (if applicable)