Constant MAX_CHECKPOINT_BYTE_COUNT

pub const MAX_CHECKPOINT_BYTE_COUNT: u64 = _; // 33_554_432u64

We limit the memory usage and download contention for each checkpoint, based on the cumulative size of the serialized blocks in the chain.

Deserialized blocks (in memory) are slightly larger than serialized blocks (on the network or disk). But they should be within a constant factor of the serialized size.