Retrospective invalidation of exec. payloads for opt. sync (#2837)

## Issue Addressed

NA

## Proposed Changes

Adds the functionality to allow blocks to be validated/invalidated after their import as per the [optimistic sync spec](https://github.com/ethereum/consensus-specs/blob/dev/sync/optimistic.md#how-to-optimistically-import-blocks). This means:

- Updating `ProtoArray` to allow flipping the `execution_status` of ancestors/descendants based on payload validity updates.
- Creating separation between `execution_layer` and the `beacon_chain` by creating a `PayloadStatus` struct.
- Refactoring how the `execution_layer` selects a `PayloadStatus` from the multiple statuses returned from multiple EEs.
- Adding testing framework for optimistic imports.
- Add `ExecutionBlockHash(Hash256)` new-type struct to avoid confusion between *beacon block roots* and *execution payload hashes*.
- Add `merge` to [`FORKS`](c3a793fd73/Makefile (L17)) in the `Makefile` to ensure we test the beacon chain with merge settings.
    - Fix some tests here that were failing due to a missing execution layer.

## TODO

- [ ] Balance tests

Co-authored-by: Mark Mackey <mark@sigmaprime.io>

beacon_node/beacon_chain/src/errors.rs

@@ -8,7 +8,7 @@ use crate::naive_aggregation_pool::Error as NaiveAggregationError;
 use crate::observed_aggregates::Error as ObservedAttestationsError;
 use crate::observed_attesters::Error as ObservedAttestersError;
 use crate::observed_block_producers::Error as ObservedBlockProducersError;
-use execution_layer::PayloadStatusV1Status;
+use execution_layer::PayloadStatus;
 use futures::channel::mpsc::TrySendError;
 use operation_pool::OpPoolError;
 use safe_arith::ArithError;
@@ -139,15 +139,27 @@ pub enum BeaconChainError {
     ExecutionLayerMissing,
     ExecutionForkChoiceUpdateFailed(execution_layer::Error),
     ExecutionForkChoiceUpdateInvalid {
-        status: PayloadStatusV1Status,
-        latest_valid_hash: Option<Vec<Hash256>>,
+        status: PayloadStatus,
     },
     BlockRewardSlotError,
     BlockRewardAttestationError,
     BlockRewardSyncError,
     HeadMissingFromForkChoice(Hash256),
     FinalizedBlockMissingFromForkChoice(Hash256),
+    InvalidFinalizedPayload {
+        finalized_root: Hash256,
+        execution_block_hash: ExecutionBlockHash,
+    },
     InvalidFinalizedPayloadShutdownError(TrySendError<ShutdownReason>),
+    JustifiedPayloadInvalid {
+        justified_root: Hash256,
+        execution_block_hash: Option<ExecutionBlockHash>,
+    },
+    ForkchoiceUpdate(execution_layer::Error),
+    FinalizedCheckpointMismatch {
+        head_state: Checkpoint,
+        fork_choice: Hash256,
+    },
 }
 
 easy_from_to!(SlotProcessingError, BeaconChainError);