More complete testing on DKG heartbeats evaluation by running encryption & decryption

[manumonti]

heartbeat_evaluation script (https://github.com/nucypher/nucypher-contracts/blob/main/scripts/evaluate_heartbeat.py) could also check if the DKG generated during heartbeat can perform a simple encryption and decryption test.

[arjunhassard]

Penalty design:

• Specific node failure attribution via Porter response
• Punishment mirrors DKG failures (i.e. 4 cumulative failures add up to 100% of reward ceded, reset every month).