chore(phpstan): enable phpstan in bundled extensions (#3667)

* feat(phpstan): pick up extended model relations typings
* feat(phpstan): pick up extended model date attributes
* feat(core): introduce `castAttribute` extender
Stops using `dates` as it's deprecated in laravel 8
* feat(phpstan): pick up extended model attributes through casts
* fix: extenders not resolved when declared namespace
* fix(phpstan): new model attributes are always nullable
* chore(phpstan): add helpful cache clearing command
* Apply fixes from StyleCI
* chore: improve extend files provider logic
* chore: rename `castAttribute` to just `cast`
* chore: update phpstan package to detect `cast` method
* chore: enable phpstan in bundled extensions
* chore: rebasing conflicts
* chore: rebasing conflicts
* chore: typings for latest 1.7 changes

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

extensions/akismet/extend.php

@@ -13,6 +13,7 @@ use Flarum\Approval\Event\PostWasApproved;
 use Flarum\Extend;
 use Flarum\Post\Event\Hidden;
 use Flarum\Post\Event\Saving;
+use Flarum\Post\Post;
 
 return [
     (new Extend\Frontend('forum'))
@@ -30,4 +31,7 @@ return [
 
     (new Extend\ServiceProvider())
         ->register(AkismetProvider::class),
+
+    (new Extend\Model(Post::class))
+        ->cast('is_spam', 'bool'),
 ];