[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 (Revert phpseclib v3 update PR #1416 (comment)).
• Cleanup CheckCredentials middleware classes.
• Fix many PHPDocs and types in line with [13.x] Support OAuth2 Server v9 #1734. This reduces over 120 PHPStan errors.
• Improve code styling and formatting.
• Fix minor bugs.
• Add more tests.