feat: improve return type for result message and enum string function

Author: lindyhopchris

src/Contracts/Toolkit/Result/Result.php

@@ -63,7 +63,8 @@ public function errors(): IListOfErrors;
     /**
      * Get the first error message, if there is one.
      *
-     * @param (Closure(UnitEnum): string)|string|null $default the default value to use if there is no error message.
+     * @param (Closure(UnitEnum): non-empty-string)|non-empty-string|null $default the default value to use if there is no error message.
+     * @return ($default is Closure|string ? non-empty-string : null)
      */
     public function error(Closure|string|null $default = null): ?string;
 

src/Toolkit/functions.php

@@ -32,6 +32,8 @@ function enum_value(int|string|UnitEnum $value): int|string
 if (!function_exists(__NAMESPACE__ . '\enum_string')) {
     /**
      * Return a string value for an enum.
+     *
+     * @return ($value is non-empty-string|UnitEnum ? non-empty-string : string)
      */
     function enum_string(string|UnitEnum $value): string
     {