feat(tree): make remove_before aware of the finalized hash (#10574)

Co-authored-by: Roman Krasiuk <rokrassyuk@gmail.com>

crates/consensus/beacon/src/engine/forkchoice.rs

@@ -75,11 +75,55 @@ impl ForkchoiceStateTracker {
         self.last_syncing.as_ref().map(|s| s.head_block_hash)
     }
 
+    /// Returns the latest received `ForkchoiceState`.
+    ///
+    /// Caution: this can be invalid.
+    pub const fn latest_state(&self) -> Option<ForkchoiceState> {
+        self.last_valid
+    }
+
+    /// Returns the last valid `ForkchoiceState`.
+    pub const fn last_valid_state(&self) -> Option<ForkchoiceState> {
+        self.last_valid
+    }
+
+    /// Returns the last valid finalized hash.
+    ///
+    /// This will return [`None`], if either there is no valid finalized forkchoice state, or the
+    /// finalized hash for the latest valid forkchoice state is zero.
+    #[inline]
+    pub fn last_valid_finalized(&self) -> Option<B256> {
+        self.last_valid.and_then(|state| {
+            // if the hash is zero then we should act like there is no finalized hash
+            if state.finalized_block_hash.is_zero() {
+                None
+            } else {
+                Some(state.finalized_block_hash)
+            }
+        })
+    }
+
     /// Returns the last received `ForkchoiceState` to which we need to sync.
     pub const fn sync_target_state(&self) -> Option<ForkchoiceState> {
         self.last_syncing
     }
 
+    /// Returns the sync target finalized hash.
+    ///
+    /// This will return [`None`], if either there is no sync target forkchoice state, or the
+    /// finalized hash for the sync target forkchoice state is zero.
+    #[inline]
+    pub fn sync_target_finalized(&self) -> Option<B256> {
+        self.last_syncing.and_then(|state| {
+            // if the hash is zero then we should act like there is no finalized hash
+            if state.finalized_block_hash.is_zero() {
+                None
+            } else {
+                Some(state.finalized_block_hash)
+            }
+        })
+    }
+
     /// Returns true if no forkchoice state has been received yet.
     pub const fn is_empty(&self) -> bool {
         self.latest.is_none()