Enable proposer boost re-orging (#2860)

## Proposed Changes

With proposer boosting implemented (#2822) we have an opportunity to re-org out late blocks.

This PR adds three flags to the BN to control this behaviour:

* `--disable-proposer-reorgs`: turn aggressive re-orging off (it's on by default).
* `--proposer-reorg-threshold N`: attempt to orphan blocks with less than N% of the committee vote. If this parameter isn't set then N defaults to 20% when the feature is enabled.
* `--proposer-reorg-epochs-since-finalization N`: only attempt to re-org late blocks when the number of epochs since finalization is less than or equal to N. The default is 2 epochs, meaning re-orgs will only be attempted when the chain is finalizing optimally.

For safety Lighthouse will only attempt a re-org under very specific conditions:

1. The block being proposed is 1 slot after the canonical head, and the canonical head is 1 slot after its parent. i.e. at slot `n + 1` rather than building on the block from slot `n` we build on the block from slot `n - 1`.
2. The current canonical head received less than N% of the committee vote. N should be set depending on the proposer boost fraction itself, the fraction of the network that is believed to be applying it, and the size of the largest entity that could be hoarding votes.
3. The current canonical head arrived after the attestation deadline from our perspective. This condition was only added to support suppression of forkchoiceUpdated messages, but makes intuitive sense.
4. The block is being proposed in the first 2 seconds of the slot. This gives it time to propagate and receive the proposer boost.


## Additional Info

For the initial idea and background, see: https://github.com/ethereum/consensus-specs/pull/2353#issuecomment-950238004

There is also a specification for this feature here: https://github.com/ethereum/consensus-specs/pull/3034

Co-authored-by: Michael Sproul <micsproul@gmail.com>
Co-authored-by: pawan <pawandhananjay@gmail.com>

beacon_node/beacon_chain/src/builder.rs

@@ -22,6 +22,7 @@ use fork_choice::{ForkChoice, ResetPayloadStatuses};
 use futures::channel::mpsc::Sender;
 use operation_pool::{OperationPool, PersistedOperationPool};
 use parking_lot::RwLock;
+use proto_array::ReOrgThreshold;
 use slasher::Slasher;
 use slog::{crit, error, info, Logger};
 use slot_clock::{SlotClock, TestingSlotClock};
@@ -31,8 +32,8 @@ use std::time::Duration;
 use store::{Error as StoreError, HotColdDB, ItemStore, KeyValueStoreOp};
 use task_executor::{ShutdownReason, TaskExecutor};
 use types::{
-    BeaconBlock, BeaconState, ChainSpec, Checkpoint, EthSpec, Graffiti, Hash256, PublicKeyBytes,
-    Signature, SignedBeaconBlock, Slot,
+    BeaconBlock, BeaconState, ChainSpec, Checkpoint, Epoch, EthSpec, Graffiti, Hash256,
+    PublicKeyBytes, Signature, SignedBeaconBlock, Slot,
 };
 
 /// An empty struct used to "witness" all the `BeaconChainTypes` traits. It has no user-facing
@@ -159,6 +160,21 @@ where
         self
     }
 
+    /// Sets the proposer re-org threshold.
+    pub fn proposer_re_org_threshold(mut self, threshold: Option<ReOrgThreshold>) -> Self {
+        self.chain_config.re_org_threshold = threshold;
+        self
+    }
+
+    /// Sets the proposer re-org max epochs since finalization.
+    pub fn proposer_re_org_max_epochs_since_finalization(
+        mut self,
+        epochs_since_finalization: Epoch,
+    ) -> Self {
+        self.chain_config.re_org_max_epochs_since_finalization = epochs_since_finalization;
+        self
+    }
+
     /// Sets the store (database).
     ///
     /// Should generally be called early in the build chain.
@@ -358,7 +374,8 @@ where
         let (genesis, updated_builder) = self.set_genesis_state(beacon_state)?;
         self = updated_builder;
 
-        let fc_store = BeaconForkChoiceStore::get_forkchoice_store(store, &genesis);
+        let fc_store = BeaconForkChoiceStore::get_forkchoice_store(store, &genesis)
+            .map_err(|e| format!("Unable to initialize fork choice store: {e:?}"))?;
         let current_slot = None;
 
         let fork_choice = ForkChoice::from_anchor(
@@ -476,7 +493,8 @@ where
             beacon_state: weak_subj_state,
         };
 
-        let fc_store = BeaconForkChoiceStore::get_forkchoice_store(store, &snapshot);
+        let fc_store = BeaconForkChoiceStore::get_forkchoice_store(store, &snapshot)
+            .map_err(|e| format!("Unable to initialize fork choice store: {e:?}"))?;
 
         let current_slot = Some(snapshot.beacon_block.slot());
         let fork_choice = ForkChoice::from_anchor(