fix: Apply CS fixer once again
ci: Don't run phpstan on test dir in the mandatory step but only in the allowed-to-fail step
style: Turn annotations into attributes
fix: Removed guards no longer necessary due to signatures or new PHP behaviour >= 8.2
fix: Implicitly nullable parameters are not explicitly nullable
style: Apply php-cs-fixer
fix: Made tests compatible with PHPUnit 12. Removed one test which was an unconditional skip for multiple years
feat: Drop dependency on horde/test and use PHPUnit 11 directly.
fix: Multiple implicit nullables
fix!: Start requiring PHP 8.0 or higher, drop outdated Stringable polyfill