Rework nbt entity data load #644

at #412 @kdcokenny wrote this comment

this skips the living entity fields from ENTITY_DATA. the mob loaders don't load Health, attributes, or active_effects, but vanilla's LivingEntity.readAdditionalSaveData does.

i tested the merged data with Age:-24000 and Health:1.0f. age applied, but the pig stayed at 10 health instead of 1. this isn't the numeric coercion issue in #559, the health tag is already a float.

But instead of doing a hot fix, we should maybe rework the system and look into doing our own, which can handle things better and easier to implement future entities