Function dynamic_technician_unbooked_for_slot 

pub fn dynamic_technician_unbooked_for_slot(
    root: &Value,
    business_id: i64,
    technician_id: i64,
    date_value: &str,
    time_value: &str,
    duration_minutes: i64,
    ignored_appointment_id: i64,
) -> bool

Returns whether one same-business technician is not already booked at a requested slot.