2.8.0-rc.2

## Changed - Once NU6.3 has activated, `proposeTransfer` and `proposefulfillingPaymentURI` propose a single payment whose value is a canonical ZIP 318 denomination (a `{1, 2, 5} * 10^k` amount between 0.01 ZEC and 10,000 ZEC) that crosses the Orchard turnstile as a ZIP 318 canoni