YWallet & Warp Sync

[tokidoki]

Relevant this grant proposal @ZcashGrants, looks like ECC will implement their own version of improved sync and integrate those into the SDK and librustzcash:

@steven-ecc

We looked at warp sync in details when we began working on an improved sync in earnest which was shortly after we packaged zcashd 5.2.0 for release. We determined then that the shortest path to an improved sync would be our own phased implementation to improve both the SDKs and the underlying librustzcash layer.