Add Packing library (#4992)

Co-authored-by: ernestognw <ernestognw@gmail.com>

test/utils/Packing.test.js

@@ -0,0 +1,27 @@
+const { ethers } = require('hardhat');
+const { expect } = require('chai');
+const { loadFixture } = require('@nomicfoundation/hardhat-network-helpers');
+const { generators } = require('../helpers/random');
+
+async function fixture() {
+  return { mock: await ethers.deployContract('$Packing') };
+}
+
+describe('Packing', function () {
+  beforeEach(async function () {
+    Object.assign(this, await loadFixture(fixture));
+  });
+
+  it('Uint128x2', async function () {
+    const first = generators.uint256() % 2n ** 128n;
+    const second = generators.uint256() % 2n ** 128n;
+    const packed = ethers.hexlify(ethers.toBeArray((first << 128n) | second));
+
+    expect(await this.mock.$asUint128x2(packed)).to.equal(packed);
+    expect(await this.mock.$asBytes32(packed)).to.equal(packed);
+    expect(await this.mock.$pack(first, second)).to.equal(packed);
+    expect(await this.mock.$split(packed)).to.deep.equal([first, second]);
+    expect(await this.mock.$first(packed)).to.equal(first);
+    expect(await this.mock.$second(packed)).to.equal(second);
+  });
+});