fix: allow int type for abstract $id property in Database\Model (#27)

It's not guaranteed that the primary key ($id here) is a string. We primarily use UUIDs for the primary key, but it could also be an integer.

Reviewed-on: https://codeberg.org/vlw/scaffold/pulls/27

src/Database/Model.php

@@ -13,7 +13,7 @@
 		public const DATE_FORMAT     = Database::DATE_FORMAT;
 		public const DATETIME_FORMAT = Database::DATETIME_FORMAT;
 
-		abstract public string $id { get; }
+		abstract public int|string $id { get; }
 
 		protected readonly Database $db;
 		private bool $_resolved = false;