feat(attachments): refactor attachment management to use attachable pivot table and update related models and tests

app/Domains/Attachable/Models/AttachableAttachment.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace App\Domains\Attachable\Models;
+
+use Illuminate\Database\Eloquent\Attributes\Fillable;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
+
+#[Fillable([
+    'attachable_type',
+    'attachable_id',
+    'attachment_id',
+])]
+class AttachableAttachment extends Model
+{
+    protected $table = 'attachable_attachments';
+
+    public $timestamps = false;
+
+    protected function casts(): array
+    {
+        return [
+            'attachable_id' => 'integer',
+            'attachment_id' => 'integer',
+        ];
+    }
+
+    /**
+     * @return MorphTo<Model, $this>
+     */
+    public function attachable(): MorphTo
+    {
+        return $this->morphTo();
+    }
+
+    /**
+     * @return BelongsTo<Attachment, $this>
+     */
+    public function attachment(): BelongsTo
+    {
+        return $this->belongsTo(Attachment::class, 'attachment_id');
+    }
+}