Write new blocks and states to the database atomically (#1285)

* Mostly atomic put_state()
* Reduce number of vec allocations
* Make crucial db operations atomic
* Save restore points
* Remove StateBatch
* Merge two HotColdDB impls
* Further reduce allocations
* Review feedback
* Silence clippy warning

beacon_node/beacon_chain/src/migrate.rs

@@ -152,7 +152,7 @@ pub trait Migrate<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>>:
             }
         }
 
-        let batch: Vec<StoreOp> = abandoned_blocks
+        let batch: Vec<StoreOp<E>> = abandoned_blocks
             .into_iter()
             .map(|block_hash| StoreOp::DeleteBlock(block_hash))
             .chain(
@@ -161,7 +161,7 @@ pub trait Migrate<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>>:
                     .map(|(slot, state_hash)| StoreOp::DeleteState(state_hash, slot)),
             )
             .collect();
-        store.do_atomically(&batch)?;
+        store.do_atomically(batch)?;
         for head_hash in abandoned_heads.into_iter() {
             head_tracker.remove_head(head_hash);
         }