Clone state ahead of block production (#4925)

* Clone state ahead of block production

* Add pruning and fix logging

* Don't hold 2 states in mem

beacon_node/beacon_chain/src/builder.rs

@@ -925,6 +925,7 @@ where
                     .map_err(|e| format!("Error initializing DataAvailabiltyChecker: {:?}", e))?,
             ),
             kzg,
+            block_production_state: Arc::new(Mutex::new(None)),
         };
 
         let head = beacon_chain.head_snapshot();