Alpenite: create a CPU DAG renderer

[adam-ce]

This super task is about writing the cpu renderer for Alpenite. We should first implement DAG-node selection and draw call generation on CPU and move it to GPU only once that works. Some parts probably should stay on CPU anyways (to have a simpler architecture), e.g. generating network requests.

Roughly, we need:

• DAG loading over the network. Given one root node, all child nodes should be found and loaded on demand. The root node should contain a good few LOD levels of child nodes. Every child node should again contain additional parts of the DAG (several levels below itself). For eviction, we need a similar strategy as in the 2.5D renderer (no missing parts between the current node and the root). this is mostly nucleus work.
• meshlet rendering: write a new geometry rendering pipeline with the gltf meshlets (maybe reuse the prototype renderer?) this is mostly engine work (webgpu or webgl). for this task, we can use a fixed set of meshlets.
• scheduled meshlet rendering: create a draw list using the parallel DAG cut algorithm