Add Multicall2 separate client

Signed-off-by: amateima <amatei@umaproject.org>

packages/sdk/src/clients/multicall2/README.md

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+# UMA Multicall2 Client
+
+This client helps you batch multiple calls together in a single transaction. Useful also for
+reducing api calls to infura when reading many properties from contracts.
+
+## Usage
+
+```js
+import { ethers } from "ethers"
+import * as uma from "@uma/sdk"
+
+// assume you have a url injected from env
+const provider = new ethers.providers.WebSocketProvider(env.CUSTOM_NODE_URL)
+
+// get the contract instance
+const client = uma.clients.multicall2.connect(address, provider)
+```

packages/sdk/src/clients/multicall2/client.e2e.ts

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+require("dotenv").config();
+import assert from "assert";
+import * as Client from "./client";
+import { ethers } from "ethers";
+import { emp } from "..";
+
+// multicall contract deployed to mainnet
+const address = "0x5ba1e12693dc8f9c48aad8770482f4739beed696";
+const empAddress = "0x4E3168Ea1082f3dda1694646B5EACdeb572009F1";
+// these require integration testing, skip for ci
+describe("multicall2", function () {
+  let client: Client.Instance;
+  let empClient: emp.Instance;
+
+  test("inits", function () {
+    const provider = ethers.providers.getDefaultProvider(process.env.CUSTOM_NODE_URL);
+    client = Client.connect(address, provider);
+    empClient = emp.connect(empAddress, provider);
+    assert.ok(client);
+    assert.ok(empClient);
+  });
+
+  test("multicall2 on emp", async function () {
+    const calls = ["priceIdentifier", "tokenCurrency", "collateralCurrency"];
+    const multicalls = calls.map((call: any) => {
+      return {
+        target: empAddress,
+        callData: empClient.interface.encodeFunctionData(call),
+      };
+    });
+    const response = await client.callStatic.aggregate(multicalls);
+    const decoded = calls.map((call: any, i: number) => {
+      const result = response.returnData[i];
+      return empClient.interface.decodeFunctionResult(call, result);
+    });
+    assert.equal(decoded.length, calls.length);
+  });
+
+  test("multicall2 on emp with no errors", async function () {
+    const calls = ["priceIdentifier", "tokenCurrency", "collateralCurrency"];
+    const multicalls = calls.map((call: any) => {
+      return {
+        target: empAddress,
+        callData: empClient.interface.encodeFunctionData(call),
+      };
+    });
+    const response = await client.callStatic.tryBlockAndAggregate(false, multicalls);
+    const decoded = calls.map((call: any, i: number) => {
+      const result = response.returnData[i].returnData;
+      return empClient.interface.decodeFunctionResult(call, result);
+    });
+    assert.equal(decoded.length, calls.length);
+  });
+
+  test("multicall2 on emp with errors", async function () {
+    const calls = ["priceIdentifier", "tokenCurrency", "disputeBondPercentage"];
+    const multicalls = calls.map((call) => {
+      return {
+        target: empAddress,
+        callData: empClient.interface.encodeFunctionData(call as any),
+      };
+    });
+    const response = await client.callStatic.tryBlockAndAggregate(false, multicalls);
+    const decoded = calls.map((call: any, i: number) => {
+      const result = response.returnData[i].returnData;
+      return response.returnData[i].success ? empClient.interface.decodeFunctionResult(call, result) : {};
+    });
+    assert.equal(decoded.length, calls.length);
+  });
+});

packages/sdk/src/clients/multicall2/client.ts

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+import { EthersContracts } from "@uma/core";
+import type { SignerOrProvider } from "../..";
+
+export type Instance = EthersContracts.Multicall2;
+const Factory = EthersContracts.Multicall2__factory;
+
+export function connect(address: string, provider: SignerOrProvider): Instance {
+  return Factory.connect(address, provider);
+}

packages/sdk/src/clients/multicall2/index.ts

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+export * from "./client";