PHP 8.1 Support

Fixes the IteratorAggregate method return type to enable PHP 8.1 compatibility.

Numerous updates to coding style and development workflow without any changes to the content.

What's Changed

• Fix docblock. by @sfadschm in #16
• Library Refresh by @MGatner in #24
• Refactor Tests by @MGatner in #27
• Update 7.3 Toolkit by @MGatner in #34
• Apply Code Styles by @MGatner in #35
• Fix workflows by @MGatner in #36

Full Changelog: v2.0.12...v2.0.13