fix: fix the duplicate root to slot

[GrapeBaBa]

🗒️ Description

Fix finalization pruning to handle duplicate roots by tracking all slots per root.

🔗 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.

[Copilot]

Pull request overview

This PR fixes a bug in finalization pruning where duplicate block roots in historical data (e.g., ZERO_HASH for missed slots) would cause incorrect pruning of pending justifications. The fix tracks all slots associated with each root rather than just one, ensuring that justifications are preserved if any associated slot remains after the finalized boundary.

Changes:

• Modified process_attestations to track all slots per root using dict[Bytes32, list[Slot]] instead of dict[Bytes32, Slot]
• Updated pruning logic to check if any slot for a root is beyond the finalized boundary
• Added test coverage for the duplicate roots scenario

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/lean_spec/subspecs/containers/state/state.py	Fixed root-to-slot mapping to handle duplicate roots by storing all slots per root, and updated pruning logic to check all slots
tests/lean_spec/subspecs/containers/test_state_justified_slots.py	Added test case to verify duplicate roots are handled correctly during finalization, and updated imports to include required types and helpers

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[tcoratger]

I've checked to run this test locally on the main branch without your fix and it works so I think it doesn't test the right thing regarding your fix in this PR.