Renderer service

[marceline-cramer]

Creates a new hearth-renderer crate and exposes as much as is feasible of the rend3 and rend3-routine APIs to guests through a message protocol.

• add initial renderer protocol to hearth-types
• add initial hearth-renderer crate
• add JsonAssetLoader helper trait and blanket AssetLoader impl
• implement Rend3Command for modifying global rend3 state
• load skyboxes
• change ambient lighting
• define stub asset loaders for materials, meshes, textures, and cube textures
• define protocol for some minimal set of texture data and implement loading
• spawn objects and handle object updates
• define protocol for full mesh data and implement loading
• somehow allow asset loaders to load from other asset loaders
• remove hardcoded directional light
• spawn directional light processes and handle light updates
• use export_to for cleaner instance spawning
• base64-encode bulky data
• use the time PR's spawn utils for instances
• validate every asset type

Follow-up:

• improve compilation speed of asset loaders?
• define protocol for full rend3 support of texture data and implement loading
• generate texture mips?
• support batched object spawns
• define protocol for full material processing and implement loading
• point lights
• write a kindling-host API

[airidaceae]

Looks great! I'm going to approve this because I would be happy merging it but I think that one helper function would be nice to have beforehand.