[avalanche] Deterministically select a payout script from the previous block hash

Summary: This picks a proof payout script deterministically, after some filtering to ensure a consistent state accross the nodes. This also includes a range selection around the winner to allow for some slack in the selection algorithm.

Test Plan:

ninja check-avalanche

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Subscribers: PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14414