More strict static checks + update on PHP 8.3

[tomtomklima]

• [x] upgrade to PHP 8.3 in code
• [x] https://github.com/phpstan/phpstan-strict-rules
• [x] https://github.com/shipmonk-rnd/composer-dependency-analyser
• [x] remove redis failchecks
• [x] update phpunit
• [x] update phinx + symfony console
• [x] make classes readonly if possible
• [x] try https://packagist.org/packages/shipmonk/phpstan-rules
• [ ] try custom "dont do new DateTIme()" https://phpstan.org/developing-extensions/rules

[tomtomklima]

done

[tomtomklima]

mostly done, closing