Anti-fee-sniping in taproot transactions.

Would have wallets vary a timing setting in Taproot payments so ordinary payments and contract closures look alike.

Wallets add a setting that stops a payment being mined before the next block, to discourage miners from re-mining recent blocks to grab fees. This would have them pick one of two ways of doing it at random. Lightning and similar contracts sometimes close using the second way, so they would blend in with everyday payments.