CheckpointExecutor is a Node component that executes all checkpoints for the
given epoch. It acts as a Consumer to StateSync
for newly synced checkpoints, taking these checkpoints and
scheduling and monitoring their execution. Its primary goal is to allow
for catching up to the current checkpoint sequence number of the network
as quickly as possible so that a newly joined, or recovering Node can
participate in a timely manner. To that end, CheckpointExecutor attempts
to saturate the CPU with executor tasks (one per checkpoint), each of which
handle scheduling and awaiting checkpoint transaction execution.