This adds a function to generate 10 stakes per block, by splitting each
coinbase transaction into 10 UTXOs, instead of using a whole coinbase
UTXO for each stake.
It makes it possible to generate more stakes that are above the dust threshold limit. Coinbase UTXOs are only valid up to block 900 on regtest, due to halvings every 150 blocks.
This fixes the test failure in D9345, when testing a proof with 1000 stakes.