Minor cleanups.

Nothing major here, the return type was inferred previously and now it is explicit and returning a promise from an async function is functionally equivalent to awaiting the promise and returning the result, just less clear what is an async call and what isn't.

source/block-reconciler.ts

@@ -45,13 +45,13 @@ const rollback = async <TBlock extends Block>(blockHistory: BlockHistory<TBlock>
  return blockHistory;
 }
 
-const backfill = async <TBlock extends Block>(getBlockByHash: GetBlockByHash<TBlock>, blockHistory: BlockHistory<TBlock>, newBlock: TBlock, onBlockAdded: (block: TBlock) => Promise<void>, onBlockRemoved: (block: TBlock) => Promise<void>, blockRetention: number) => {
+const backfill = async <TBlock extends Block>(getBlockByHash: GetBlockByHash<TBlock>, blockHistory: BlockHistory<TBlock>, newBlock: TBlock, onBlockAdded: (block: TBlock) => Promise<void>, onBlockRemoved: (block: TBlock) => Promise<void>, blockRetention: number): Promise<BlockHistory<TBlock>> => {
  if (newBlock.parentHash === "0x0000000000000000000000000000000000000000000000000000000000000000")
- return rollback(blockHistory, onBlockRemoved);
+ return await rollback(blockHistory, onBlockRemoved);
  const parentBlock = await getBlockByHash(newBlock.parentHash);
  if (parentBlock === null) throw new Error("Failed to fetch parent block.");
  if (parseInt(parentBlock.number, 16) + blockRetention < parseInt(blockHistory.last().number, 16))
- return rollback(blockHistory, onBlockRemoved);
+ return await rollback(blockHistory, onBlockRemoved);
  blockHistory = await reconcileBlockHistory(getBlockByHash, blockHistory, parentBlock, onBlockAdded, onBlockRemoved, blockRetention);
  return await reconcileBlockHistory(getBlockByHash, blockHistory, newBlock, onBlockAdded, onBlockRemoved, blockRetention);
 }