Laravel Nested Sets v7 - Laravel 11, PHP 8.3, PHPUnit 10.* and drop EOL PHP support

[asurcodes]

Changes proposed in this PR:

• Update master branch with latest changes
• Add support for Laravel 11
• Drop backwards compatibility for EOL PHP versions (other releases still available)
• Upgrade PHPUnit to version 10.* (config file migration required)
• Upgrade deprecated ccheckout action to v4
• Add namespacing to test models
• Other minor style consistency changes

I let to @lazychaser if this qualifies for a major version bump. If you need any changes or have any suggestions let me know! 😄