2108 - Create collsion_damage

Create a type to gather damage ring buffer (position, time, amount) for a pair of grid types. Pairs to be tested: hero_bullets vs. enemy_instances enemy_bullets vs. hero_instances hero_instances vs. enemy_instances Also: Rename “ref” in schema to “context” (two names for the same concept.) Rename “collision_source_types” to “collision_source_radius” for clarity.