refactor: replace magic numbers with constants

Author: kenjis

system/Database/Exceptions/DatabaseException.php

@@ -20,5 +20,5 @@ class DatabaseException extends Error implements ExceptionInterface
      *
      * @var int
      */
-    protected $code = 8;
+    protected $code = EXIT_DATABASE;
 }

system/Exceptions/CastException.php

@@ -23,11 +23,11 @@ class CastException extends CriticalError
     use DebugTraceableTrait;
 
     /**
-     * Error code
+     * Exit status code
      *
      * @var int
      */
-    protected $code = 3;
+    protected $code = EXIT_CONFIG;
 
     public static function forInvalidJsonFormatException(int $error)
     {

system/Exceptions/ConfigException.php

@@ -19,11 +19,11 @@ class ConfigException extends CriticalError
     use DebugTraceableTrait;
 
     /**
-     * Error code
+     * Exit status code
      *
      * @var int
      */
-    protected $code = 3;
+    protected $code = EXIT_CONFIG;
 
     public static function forDisabledMigrations()
     {