Prioritize use of `ReturnAttr`

[rodber]

If ReturnAttr is used in main method for a given Action (job), the Workflow system should consider that definition instead of the default public static function return():.

[rodber]

recurringPrice: sync(
    new class() extends Action {
        #[ReturnAttr(
            new IntAttr(min: 1)
        )]
        protected function main(
            bool $isAnnual,
            #[IntAttr(min: 0)]
            int $recurring_price_month,
            #[IntAttr(min: 0)]
            int $recurring_price_year,
        ): int {
            return $isAnnual ? $recurring_price_year : $recurring_price_month;
        }
    },
    isAnnual: variable('isAnnual'),
    recurring_price_year: response('plan', 'recurring_price_year'),
    recurring_price_month: response('plan', 'recurring_price_month'),
),