Measured block propagation delay in seconds. This will determine the
conservative window when we measure confirmation risk internally in
the consensus layer.
The threshold controlling whether a node is in catch-up mode.
A node is in catch-up mode if its local best epoch number is
CATCH_UP_EPOCH_LAG_THRESHOLD behind the median of the epoch
numbers of peers.
The threshold controlling whether we should query local_block_info in
disk when requesting block header or block. If the difference
between height of the block and current best height is less than
LOCAL_BLOCK_INFO_QUERY_THRESHOLD, we can request block directly through
network, otherwise we should check disk first.