What is the ruling on taking a sum of money that was donated to a charitable project as a perpetual charity (Sadaqah Jariyah), after finding it on the road during Hajj, and is it obligatory to donate it within Mecca?

Picking up a lost item in the Haram (definition) (sacred precinct) is no different from picking one up in the "hill" (non-sacred area). If the lost item is insignificant, the finder may do with it as they wish. The insignificance of an item is determined by time and place. If the finder does not know the owner of the insignificant lost item, they may benefit from it or give it away in charity.