Rollback account and discard transaction after N blocks

[SantiagoPittella]

Related to: #607 (comment)

One potential solution is to establish a block threshold for pending transactions to be committed. During a sync operation, we can then examine the database for these pending transactions and mark them as discarded if they exceed the defined block threshold.

A block threshold should be in place, and after a sync, we can check if any pending transaction passed the threshold. In that case, the transaction should be marked as discarded and a rollback to the account should be applied.

[igamigo]

Adding this comment for reference here as well:

Yes, I think for now we can define a threshold of say, 10 blocks to determine whether a transaction can be marked as "stale" or discard it altogether. In the future we might want to store metadata from this transaction. For example, if we define a transaction expiration of 3 blocks, we can store it and then locally update the transaction appropriately.