fix: pass serialized data in notification.deleted event to avoid Deserialisation (#13061)

https://one.newrelic.com/alerts/issue?account=3437125&duration=259200000&state=d088e9b7-d0ce-3fcf-fda5-145df8b9cb2a


## Description
Pass serialized data instead of ActiveRecord object in
dispatch_destroy_event to prevent ActiveJob::DeserializationError when
the notification is already deleted.

This error occurs frequently because RemoveDuplicateNotificationJob
deletes notifications, and by the time the async EventDispatcherJob
runs, the record no longer exists.

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?



## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Avoids ActiveJob deserialization failures by sending serialized data
for notification deletion and updating the listener accordingly.
> 
> - `Notification#dispatch_destroy_event` now dispatches
`NOTIFICATION_DELETED` with serialized `notification_data` (`id`,
`user_id`, `account_id`) instead of the AR object
> - `ActionCableListener#notification_deleted` reads
`notification_data`, finds `User`/`Account`, computes
`unread_count`/`count` via `NotificationFinder`, and broadcasts using
the user’s pubsub token
> - Specs updated to pass `notification_data` and assert payload
(including `unread_count`/`count`)
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
e2ffbe765b148fdfd2cd2e031c657c36e423c1f5. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Vishnu Narayanan <iamwishnu@gmail.com>

app/models/notification.rb

@@ -180,7 +180,17 @@ class Notification < ApplicationRecord
   end
 
   def dispatch_destroy_event
-    Rails.configuration.dispatcher.dispatch(NOTIFICATION_DELETED, Time.zone.now, notification: self)
+    # Pass serialized data instead of ActiveRecord object to avoid DeserializationError
+    # when the async EventDispatcherJob runs after the notification has been deleted
+    Rails.configuration.dispatcher.dispatch(
+      NOTIFICATION_DELETED,
+      Time.zone.now,
+      notification_data: {
+        id: id,
+        user_id: user_id,
+        account_id: account_id
+      }
+    )
   end
 
   def set_last_activity_at