algod importer: More resilient node swapping.

[winder]

Problem

If algod is swapped out while Conduit is running, it might be slightly out of date and need to have the sync round updated (or run fast catchup.

Solution

Check if node needs to catchup during GetBlock.

If a retry is detected, run the catchupNode function. This should not be run unless absolutely necessary to avoid introducing additional latency.