Question for all the zcash people out there Back in the early days of Zcash - sapling and such - one of the fundamental problems with achieving functional privacy was that you had to download the entire blockchain to your device in order to produce the zk proof associated with a shielded transaction. this made sense, because you need the entire history of transactions to be able to prove that you currently own unspent UTXOs Has this problem been solved without introducing a trusted 3rd party? if so, how? if not, how is Zashi managing this?