Release 1.2.3

What's Changed

• Migrate to PHP 8.1 as default version by @RikudouSage in #33
• Use newer phpstan and rector, use php 8.1 features by @RikudouSage in #34
• Add readonly to properties by @RikudouSage in #36

Full Changelog: v1.2.280...v1.2.381