feat: add Keypair class and deprecate Account (#17098)

* feat: add Keypair class and deprecate Account

* chore: fix lint issues

* chore: rename TransactionSigner to Signer

web3.js/test/keypair.test.ts

@@ -0,0 +1,50 @@
+import {expect} from 'chai';
+import {Buffer} from 'buffer';
+
+import {Keypair} from '../src';
+
+describe('Keypair', () => {
+  it('generate new keypair', () => {
+    const keypair = Keypair.generate();
+    expect(keypair.secretKey).to.have.length(64);
+  });
+
+  it('create keypair from secret key', () => {
+    const secretKey = Buffer.from(
+      'mdqVWeFekT7pqy5T49+tV12jO0m+ESW7ki4zSU9JiCgbL0kJbj5dvQ/PqcDAzZLZqzshVEs01d1KZdmLh4uZIg==',
+      'base64',
+    );
+    const keypair = Keypair.fromSecretKey(secretKey);
+    expect(keypair.publicKey.toBase58()).to.eq(
+      '2q7pyhPwAwZ3QMfZrnAbDhnh9mDUqycszcpf86VgQxhF',
+    );
+  });
+
+  it('creating keypair from invalid secret key throws error', () => {
+    const secretKey = Buffer.from(
+      'mdqVWeFekT7pqy5T49+tV12jO0m+ESW7ki4zSU9JiCgbL0kJbj5dvQ/PqcDAzZLZqzshVEs01d1KZdmLh4uZIG==',
+      'base64',
+    );
+    expect(() => {
+      Keypair.fromSecretKey(secretKey);
+    }).to.throw('provided secretKey is invalid');
+  });
+
+  it('creating keypair from invalid secret key succeeds if validation is skipped', () => {
+    const secretKey = Buffer.from(
+      'mdqVWeFekT7pqy5T49+tV12jO0m+ESW7ki4zSU9JiCgbL0kJbj5dvQ/PqcDAzZLZqzshVEs01d1KZdmLh4uZIG==',
+      'base64',
+    );
+    const keypair = Keypair.fromSecretKey(secretKey, {skipValidation: true});
+    expect(keypair.publicKey.toBase58()).to.eq(
+      '2q7pyhPwAwZ3QMfZrnAbDhnh9mDUqycszcpf86VgQxhD',
+    );
+  });
+
+  it('generate keypair from random seed', () => {
+    const keypair = Keypair.fromSeed(Uint8Array.from(Array(32).fill(8)));
+    expect(keypair.publicKey.toBase58()).to.eq(
+      '2KW2XRd9kwqet15Aha2oK3tYvd3nWbTFH1MBiRAv1BE1',
+    );
+  });
+});