Refrain from PoP mining of old keystone blocks

[Leonardiae]

Confirmation

• I have checked for similar issues.

Describe the bug

Since mining older blocks increases the risk of spending fees while being too late to be eligable for a reward I think the PoP miner should refrain from mining older keystone blocks.

Also because you risk to mine those blocks again in case you restart the PoP miner and already mined the earlier keystone blocks in previous session.

Expected behaviour

Check the current block and what latest keystone block is, set that as the last known keystone and don't mine that anymore.

Environment

Version:
Operating System:
Architecture:

Additional Information

I started a PoP miner while latest block was 1315551.
When block 1315575 is being detected, the PoP miner starts mining block 1315575, 1315550 and 1315525. I think it should only mine 1315575 and not 1315550 and 1315525 anymore.