Load chunks per-region in Scene#loadChunks

[NotStirred]

Merge after #1256

Rather than loading chunks in the order they appear in the chunk list, now load chunks region by region, which should lead to much better region loading performance, also the task scheduling has been cleaned up. Maybe some minor improvements cache-wise for the octree due to loading chunks close to each other too

Still need to create some ChunkData cache, as each chunk currently allocates one

[NotStirred]

Should now be ready for review!

[NotStirred]

wait I really bricked it and didn't realise

[ShirleyNekoDev]

Required PR is merged, therefore I assume that this one is ready once the conflicts are resolved? 🔥