This technically has a TOCTOU where we sync an Epoch's metadata (signifying we
did sync to that point), then check if the Router was deployed, yet at that
very moment the node resets to genesis. By ensuring the Router is deployed, we
avoid this (and don't need to track the deployment block in-contract).
Also uses a JoinSet to sync the 32 blocks in parallel.
The caller is paid a fixed fee per unit of gas spent. That arguably
incentivizes the publisher to raise the gas used by internal calls, yet this
doesn't effect the user UX as they'll have flatly paid the worst-case fee
already. It does pose a risk where callers are arguably incentivized to cause
transaction failures which consume all the gas, not just increased gas, yet:
1) Modern smart contracts don't error by consuming all the gas
2) This is presumably infeasible
3) Even if it was feasible, the gas fees gained presumably exceed the gas fees
spent causing the failure
The benefit to only paying the callers for the gas used, not the gas alotted,
is it allows Serai to build up a buffer. While this should be minor, a few
cents on every transaction at best, if we ever do have any costs slip through
the cracks, it ideally is sufficient to handle those.
