Remove Validator Balance Requirement for Checkpoints

[karlem]

Find a way to remove the need for validators to maintain a balance of circulating supply in order to create checkpoints.

Suggestion: Validators could receive automatic fund allocations from the network to cover the necessary balance.

[raulk]

IUC, the issue is that these signatures are sent as ordinary transactions in the subnet. The FVM verifies that the sender account exists and has sufficient balance to cover the maximum gas costs as per base fee and gas fee cap. What we could do:

1. Auto-create Eth accounts matching the secp256k1 public keys of validators at genesis and as new validators are added.
2. Make validators submit these transactions from their f410 identities.
3. Detect "system" transactions like this at the interpreter level through pattern matching, e.g.:
   • from == some validator address.
   • to == gateway.
   • data is ABI-encoded to addCheckpointSignature.
4. Execute those transactions as implicit transactions at the FVM level; this disarms gas charging and removes the need for the account to hold balance.

We will need to accompany this with rejecting the block if the validator spams or misuses the system, e.g. includes transactions satisfying the above but with non-zero exit codes (error).

We'd need to make changes to the mempool to accept such transactions at that level too.