feat: add robust puppeteer login helper with captcha support

[NikkiAung]

This PR introduces a new login() context helper for both PlaywrightCrawler and PuppeteerCrawler that automatically handles website login forms. The helper supports both single-step login flows (where username and password fields are visible together) and two-step flows (where users must click "Next" after entering username). It includes smart field detection with customizable locators, robust success detection, and optional captcha handling with timeout protection.

Key features: Automatic form detection, custom locators, captcha integration, comprehensive error handling, and extensive test coverage (52 total tests across both crawlers). The helper gracefully handles cases where no login form is found and provides clear error messages for debugging.

async requestHandler({ login }) {
    await login({
        username: '[email protected]',
        password: 'password123',
        handleCaptcha: async (page) => {
            // Solve captcha here
        },
    });
}

Resolves full features for Puppeteer #3040