[13.x] Cleanup, improve types and tests

[hafezdivandari]

This PR does the following improvements without any behavioral change:

• Prepare for PHP 8.4 support.
• Cleanup removed phpseclib package's classes from passport:keys command (https://github.com/laravel/passport/issues/1416#issuecomment-787828856).
• Cleanup CheckCredentials middleware classes.
• Fix many PHPDocs and types in line with #1734. This reduces over 120 PHPStan errors.
• Improve code styling and formatting.
• Fix minor bugs.
• Add more tests.