feat: add tiered attestation scoring

[perfogic]

What was wrong?

Closes #1437. Ream only had the round-based block builder. leanSpec #1149 adds a tiered selection strategy that prioritizes attestations by Finalize > Justify > Build.

What has been done

• Added a --block-production <round-based|tiered> flag (default round-based) to pick the strategy at runtime.
• Ported the tiered scoring logic with tests for tier ordering, proof-union emission, and an end-to-end smoke test.

What need to know

• build_block dispatches on the strategy; see select_tiered and seal_block.
• Ream does not keep aggregated_payloads as global state. on_block stores proofs by (validator_id, data_root), so select_tiered rebuilds the proof pool before scoring.
• The selector does not run select_proofs_for_coverage; proof selection/compaction are delegated to select_aggregated_proofs + compact_aggregated_proofs. Because of that, select_tiered emits the full proof union while scoring/projection use only new_voters.

To-Do

• I have read CONTRIBUTING.md.
• This PR title follows conventional commits.

[shariqnaiyer]

Please make this modular as per
leanEthereum/leanSpec#1149

[shariqnaiyer]

I will leave the architecture of how you want to select the strategy up to your judgement

[perfogic]

great, thanks. Will follow the modular 👍

[shariqnaiyer]

@perfogic please rebase

[Kayden-ML]

Looks good nice work I just gave this through review but can you run make pr before this is merged into master so it updates the book-cli-check

[perfogic]

@Kayden-ML Thanks for reviewing, i ran make pr and updated the check-cli-docs output.