Fix PHPStan errors: new static() in trait and Eloquent method access on interface

- Add @phpstan-consistent-constructor to SubscribableMailMessage so that
  new static() inside the SubscribableNotification trait is recognised as
  safe. Without this annotation PHPStan cannot verify that subclasses share
  the same constructor signature.

- Add is_a($modelClass, Model::class, true) to the UnsubscribeController
  guard so PHPStan narrows $modelClass to class-string<Model> in addition
  to class-string<CanUnsubscribe>. Larastan knows Model declares where() and
  getRouteKeyName(), eliminating the two 'method.notFound' errors. The check
  is also correct at runtime: subscribers must be Eloquent models.

https://claude.ai/code/session_01R4pAjWwGY8xKspsdU8xnsy

Author: claude

src/Controllers/UnsubscribeController.php

@@ -2,6 +2,7 @@
 
 namespace YlsIdeas\SubscribableNotifications\Controllers;
 
+use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\Relation;
 use Illuminate\Http\Request;
 use Illuminate\Routing\Controller;
@@ -21,7 +22,9 @@ public function __invoke(Request $request, string $subscriberType, mixed $subscr
     {
         $modelClass = Relation::getMorphedModel($subscriberType) ?? $subscriberType;
 
-        if (! class_exists($modelClass) || ! is_a($modelClass, CanUnsubscribe::class, true)) {
+        if (! class_exists($modelClass)
+            || ! is_a($modelClass, CanUnsubscribe::class, true)
+            || ! is_a($modelClass, Model::class, true)) {
             abort(403, __('Could not process unsubscribe request'));
         }
 

src/Messages/SubscribableMailMessage.php

@@ -5,6 +5,7 @@
 use Illuminate\Notifications\Messages\MailMessage;
 use YlsIdeas\SubscribableNotifications\Concerns\SubscribableNotification;
 
+/** @phpstan-consistent-constructor */
 class SubscribableMailMessage extends MailMessage
 {
     use SubscribableNotification;