isBookingRangeValid(listing: Listing,date: string,days: number,holidays: Holiday[],): boolean
Whether booking days consecutive days starting on date is valid for a
daily listing: every day must be a bookable weekday, fall outside all
holidays, and stay within the listing's booking window. Used to enforce the
visitor's chosen span on "customisable days" listings at submit time, where
the day count isn't known when the date list is rendered.