Performance improvements for IPLDBlocks in eden watcher (#80)

* Avoid fetching contracts while creating a checkpoint

* Use enum for state kind and cache ipld status

* Avoid fetching block twice while finalizing a staged diff IPLDBlock

* Create checkpoints at fixed block numbers and refactor checkpointing code

* Avoid calling block handler until start block is reached

* Use delete while finalizing staged diff IPLDBlocks

* Add a check to ensure hooks job is created only once

* Avoid check for initial state while creating a checkpoint

packages/graph-node/src/watcher.ts

@@ -172,8 +172,8 @@ export class GraphWatcher {
 
     // Call block handler(s) for each contract.
     for (const dataSource of this._dataSources) {
-      // Check if block handler(s) are configured.
-      if (!dataSource.mapping.blockHandlers) {
+      // Check if block handler(s) are configured and start block has been reached.
+      if (!dataSource.mapping.blockHandlers || blockData.blockNumber < dataSource.source.startBlock) {
         continue;
       }