refactor: update code base to php 8 and set phpstan lvl to 6

app/Helpers/rss_helper.php

app/Helpers/url_helper.php

app/Libraries/ActivityPub/Activities/AnnounceActivity.php

app/Libraries/ActivityPub/ActivityRequest.php

app/Libraries/ActivityPub/Config/ActivityPub.php

app/Libraries/ActivityPub/Controllers/ActorController.php

app/Libraries/ActivityPub/Controllers/BlockController.php

app/Libraries/ActivityPub/Controllers/NoteController.php

...Libraries/ActivityPub/Controllers/WebFingerController.php

app/Libraries/ActivityPub/Core/AbstractObject.php

app/Libraries/ActivityPub/Core/ObjectType.php

app/Libraries/ActivityPub/Entities/Note.php

app/Libraries/ActivityPub/Filters/ActivityPubFilter.php

app/Libraries/ActivityPub/Helpers/activitypub_helper.php

app/Libraries/ActivityPub/HttpSignature.php

app/Libraries/ActivityPub/Models/ActivityModel.php

app/Libraries/ActivityPub/Models/ActorModel.php

app/Libraries/ActivityPub/Models/BlockedDomainModel.php

app/Libraries/ActivityPub/Models/FavouriteModel.php

app/Libraries/ActivityPub/Models/FollowModel.php