Idea: Make Entities a monoid

The book DoD talks a lot about entities merging together into a swarm to reduce computational complexity of low resolution objects.
Here's an idea : the way we compose many entities into one is by making them compose-able in the first place!

The issue names no files, tests, or entry points, and does not define acceptance criteria. Start by reviewing how the renderer currently represents and combines entities, then clarify the intended monoid operation and how completion would be validated.

Written by the indexing model from the issue text.