Use Library for Multisend (#20)

In order to have less, overall, logic in this project, we use an npm library `ethers-multisend`. The reason we hesitated before was because it uses ethers-v5, but it does not really affect our flow (just adds a few more node modules).

package.json

@@ -18,6 +18,7 @@
     "@slack/web-api": "^7.1.0",
     "@types/node": "^20.11.30",
     "ethers": "^6.12.0",
+    "ethers-multisend": "^3.1.0",
     "loglevel": "^1.9.1",
     "moment": "^2.30.1",
     "typescript": "^5.4.3",

src/billingContract.ts

@@ -1,8 +1,8 @@
 import { ethers, formatEther } from "ethers";
 import { BillingData, LatestBillingStatus, PaymentStatus } from "./types";
 import { BILLING_CONTRACT_ABI, ROLE_MODIFIER_ABI } from "./abis";
-import { MetaTransaction, encodeMulti } from "./multisend";
 import { getTxCostForGas, maxBigInt } from "./gas";
+import { MetaTransaction, encodeMulti } from "ethers-multisend";
 
 interface BillingInput {
   addresses: `0x${string}`[];
@@ -151,7 +151,7 @@ export class BillingContract {
         account,
         amount,
       ]),
-      value: 0,
+      value: "0",
       operation: 0,
     };
   }
@@ -187,7 +187,7 @@ export class BillingContract {
         amount,
         feeRecipient,
       ]),
-      value: 0,
+      value: "0",
       operation: 0,
     };
   }