improve: Add optional destination parameter to ILogInAs

[petarbasic]

Summary

• Adds an optional destination parameter to ILogInAs to control the post-login redirect
• Can be used to avoid being redirected to the admin dashboard after login, which renders views blocks that can cause race conditions during parallel test execution
• Backwards compatible: existing callers are unaffected (no destination = default Drupal behavior)

Usage

// Default behavior (no change):
ILogInAs([page, 'dru_admin'])

// Skip dashboard redirect (for parallel tests):
ILogInAs([page, 'dru_admin', '/user'])