Move the model callbacks into Observables; reduce caching since it held balances incorrectly

app/Models/Observers/AircraftObserver.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace App\Models\Observers;
+
+use App\Models\Aircraft;
+use App\Support\ICAO;
+
+/**
+ * Class AircraftObserver
+ * @package App\Models\Observers
+ */
+class AircraftObserver
+{
+    public function creating(Aircraft $aircraft): void
+    {
+        if (empty($aircraft->hex_code)) {
+            $aircraft->hex_code = ICAO::createHexCode();
+        }
+    }
+}