The next commit requires an additional mainnet block which changes the difficulty.
Also fix a few minor mistakes in the test (suite):
- rename the create_coinbase retarger_period argument to halving_period. Before bitcoin#31583 this was hardcoded for regtest where these values are the same.
- drop unused fees argument from mine helper
Finally the CPU miner instructions for generating the alternative mainnet chain are expanded.
Github-Pull: #33446
Rebased-From: 4c3c1f42cf
