✨ Add attendee count helpers and enhance Meetup API responses

- ➕ Introduce `attendeesCount` and `mightAttendeesCount` methods in `MeetupEvent` model for cleaner attendee calculations.
- 🛠️ Refactor API responses to use attendee count helpers in `Meetup` and `MeetupEventController`.
- 🧪 Update tests to validate JSON structure with attendee-related fields (`id`, `attendees`, `might_attendees`).

app/Models/Meetup.php

@@ -272,8 +272,8 @@ class Meetup extends Model implements HasMedia
                 'location' => $nextEvent->location,
                 'description' => $nextEvent->description,
                 'link' => $nextEvent->link,
-                'attendees' => count($nextEvent->attendees ?? []),
-                'might_attendees' => count($nextEvent->might_attendees ?? []),
+                'attendees' => $nextEvent->attendeesCount(),
+                'might_attendees' => $nextEvent->mightAttendeesCount(),
                 'nostr_note' => str($nextEvent->nostr_status)->after('Sent event ')->before(' to '),
             ] : null,
         );