Enforce Optimistic Sync Conditions & CLI Tests (v2) (#3050)

## Description

This PR adds a single, trivial commit (f5d2b27d78) atop #2986 to resolve a tests compile error. The original author (@ethDreamer) is AFK so I'm getting this one merged ☺️ 

Please see #2986 for more information about the other, significant changes in this PR.


Co-authored-by: Mark Mackey <mark@sigmaprime.io>
Co-authored-by: ethDreamer <37123614+ethDreamer@users.noreply.github.com>

consensus/fork_choice/src/fork_choice.rs

@@ -928,6 +928,54 @@ where
             .is_descendant(self.fc_store.finalized_checkpoint().root, block_root)
     }
 
+    /// Returns `Ok(false)` if a block is not viable to be imported optimistically.
+    ///
+    /// ## Notes
+    ///
+    /// Equivalent to the function with the same name in the optimistic sync specs:
+    ///
+    /// https://github.com/ethereum/consensus-specs/blob/dev/sync/optimistic.md#helpers
+    pub fn is_optimistic_candidate_block(
+        &self,
+        current_slot: Slot,
+        block_slot: Slot,
+        block_parent_root: &Hash256,
+        spec: &ChainSpec,
+    ) -> Result<bool, Error<T::Error>> {
+        // If the block is sufficiently old, import it.
+        if block_slot + spec.safe_slots_to_import_optimistically <= current_slot {
+            return Ok(true);
+        }
+
+        // If the justified block has execution enabled, then optimistically import any block.
+        if self
+            .get_justified_block()?
+            .execution_status
+            .is_execution_enabled()
+        {
+            return Ok(true);
+        }
+
+        // If the block has an ancestor with a verified parent, import this block.
+        //
+        // TODO: This condition is not yet merged into the spec. See:
+        //
+        // https://github.com/ethereum/consensus-specs/pull/2841
+        //
+        // ## Note
+        //
+        // If `block_parent_root` is unknown this iter will always return `None`.
+        if self
+            .proto_array
+            .iter_nodes(block_parent_root)
+            .any(|node| node.execution_status.is_valid())
+        {
+            return Ok(true);
+        }
+
+        Ok(false)
+    }
+
     /// Return the current finalized checkpoint.
     pub fn finalized_checkpoint(&self) -> Checkpoint {
         *self.fc_store.finalized_checkpoint()