Add updated get_eth1_vote function for electra (#4106)

specs/electra/validator.md

@@ -153,6 +153,40 @@ def get_eth1_pending_deposit_count(state: BeaconState) -> uint64:
         return uint64(0)
 ```
 
+*Note*: Clients will be able to remove the `Eth1Data` polling mechanism in an uncoordinated fashion once the transition period is finished. The transition period is considered finished when a network reaches the point where `state.eth1_deposit_index == state.deposit_requests_start_index`.
+
+```python
+def get_eth1_vote(state: BeaconState, eth1_chain: Sequence[Eth1Block]) -> Eth1Data:
+    # [New in Electra:EIP6110]
+    if state.eth1_deposit_index == state.deposit_requests_start_index:
+        return state.eth1_data
+
+    period_start = voting_period_start_time(state)
+    # `eth1_chain` abstractly represents all blocks in the eth1 chain sorted by ascending block height
+    votes_to_consider = [
+        get_eth1_data(block) for block in eth1_chain
+        if (
+            is_candidate_block(block, period_start)
+            # Ensure cannot move back to earlier deposit contract states
+            and get_eth1_data(block).deposit_count >= state.eth1_data.deposit_count
+        )
+    ]
+
+    # Valid votes already cast during this period
+    valid_votes = [vote for vote in state.eth1_data_votes if vote in votes_to_consider]
+
+    # Default vote on latest eth1 block data in the period range unless eth1 chain is not live
+    # Non-substantive casting for linter
+    state_eth1_data: Eth1Data = state.eth1_data
+    default_vote = votes_to_consider[len(votes_to_consider) - 1] if any(votes_to_consider) else state_eth1_data
+
+    return max(
+        valid_votes,
+        key=lambda v: (valid_votes.count(v), -valid_votes.index(v)),  # Tiebreak by smallest distance
+        default=default_vote
+    )
+```
+
 #### Execution payload
 
 `prepare_execution_payload` is updated from the Deneb specs.