fix use updated finalized_slot for justifiability

[bomanaps]

🗒️ Description

The justifiability checks were using self.latest_finalized.slot which remains immutable during attestation processing, causing different finalization behavior when votes are packed in one block versus spread across multiple blocks, this fix changes lines 489 and 543 to use the mutable finalized_slot variable that gets updated when finalization advances mid-loop, this aligns with the original 3sf-mini spec behavior at https://github.com/ethereum/research/blob/master/3sf-mini/consensus.py where state.latest_finalized_slot is updated and immediately visible to subsequent votes in the same block.

🔗 Related Issues or PRs

✅ Checklist

• Ran tox checks to avoid unnecessary CI fails:

  uvx tox

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

[tcoratger]

@bomanaps To avoid this behaviour to happen again, could we have a simple unit test or even better a test vector to flag this behaviour? Meaning a test that didn't pass before and that passes now.

[bomanaps]

@bomanaps To avoid this behaviour to happen again, could we have a simple unit test or even better a test vector to flag this behaviour? Meaning a test that didn't pass before and that passes now.

Added the test vector