Chunks need to be compacted with their neighbors when they get inserted into a ChunkStore, so that all the runtime arrow downcast/introspection-related fixed costs can be amortized.

This is a pre-requirement to drop the deserialization cache, which is a requirement for megahertz logging.

There an infinite amount of subtlety to this, but for now we only want to focus on the very happy path (i.e.: make logging scalars nice).