fix(storage): store fork-choice votes independently (#552)

## 🗒️ Description / Motivation

This PR fixes fork-choice vote tracking so validator votes are stored
independently from aggregated proofs and gossip signatures.

Previously, fork-choice votes were derived from bounded in-memory
proof/signature buffers. When those buffers evicted old entries through
FIFO cleanup, a validator’s latest vote could disappear even though the
vote should still count for fork choice. This PR adds a separate
proof-less vote store so fork-choice weights are not affected by
proof/signature retention.

## What Changed

- Updated `crates/storage/src/store.rs`
  - Added an independent latest-vote store keyed by validator index.
- Records known fork-choice votes when aggregated payloads become known.
- Records block-included attestation votes separately from proof
storage.
  - Keeps proof buffers for aggregation/proposal behavior only.
  - Prunes stored votes once their target is finalized.

- Updated `crates/blockchain/src/store.rs`
- Inserts block-included attestation votes into the independent vote
store during block processing.

## Correctness / Behavior Guarantees

- Fork-choice votes no longer disappear when proof or signature buffers
evict entries.
- Existing proof/signature buffer behavior is preserved for aggregation
and block proposal.
- Latest-vote selection keeps the existing rule: higher slot wins, and
same-slot ties use the canonical attestation-data root.
- Finalized-target votes are pruned once they can no longer affect fork
choice.

## Tests Added / Run

- Added regression coverage for votes surviving aggregated proof FIFO
eviction.
- Added coverage for pruning finalized-target votes from the independent
vote store.

## Related Issues / PRs
- Closes #504 

## ✅ Verification Checklist

- [x] Ran `make fmt` — clean
- [x] Ran `make lint` (clippy with `-D warnings`) — clean
- [x] Ran `make test` (`cargo test --workspace --profile release-fast`)
— all passing

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Co-authored-by: Tomás Grüner <47506558+MegaRedHand@users.noreply.github.com>

Author: dicethedev