Smart block deconstruction

[anshalshukla]

🗒️ Description

We were doing naive deconstruction of all the blocks that were being imported, instead we can only focus on attestations that can have source as state's latest justified as those can be packed to move chain's justified and finalized ahead.

🔗 Related Issues or PRs

✅ Checklist

• Ran local quality checks to avoid unnecessary CI fails:

  just check

• Considered adding appropriate tests for the changes.
• Considered updating the online docs in the ./docs/ directory.