feat: uniq FastUsdcTransaction id

Author: turadg

schema.graphql

@@ -25,7 +25,7 @@ enum FastUsdcTransactionStatus {
 }
 
 type FastUsdcTransaction @entity {
-  id: ID!
+  id: ID! @index(unique: true)
   """
   EVM address from which the USCD funds originated
   """

src/mappings/events/fastUsdc.ts

@@ -21,6 +21,8 @@ export const transactionEventKit = (block: CosmosBlock, data: StreamCell, module
     const { height } = block.header;
     const time = block.header.time as Date;
 
+    // XXX this assumes that records will be processed in order,
+    // so multiple indexer workers is not supported.
     const t = await FastUsdcTransaction.get(id);
     if (!t) {
       if (payload.status !== FastUsdcTransactionStatus.OBSERVED) {