* Fix extension freshrss_user_maintenance in actualize_script
Follow-up of https://github.com/FreshRSS/FreshRSS/pull/3440
The hook was called before registering all the extensions for the current user
* PHPStan Level 6 for extensions
And remove 5-year old legacy format of enabled extensions < FreshRSS 1.11.1
* Fix multiple bugs in extensions
* Minor typing
* Don't change signature of methods supposed to be overridden
* PHPStan Level 9 and compatibility Intelliphense
* Set as final the methods not supposed to be overriden