Tree remover performance improvements

[CptCrispyCrunchy]

In dense forested area the game slows down significantly. Part of it is of course the bigger work for the BlockBufferSystem, but there are also improvements to be done when iterating over the trees and regions.

[skaldarnar]

The block buffer utilized by the tree removal system blows up very fast, and thus the remove operations for placed blocks becomes very inefficient. Additionally, many blocks/block positions seem to be added multiple times.

I did some experiments with a new WorldProviderCore#setBlocks(Map<Vector3i, Block> blocks) (sets multiple blocks before marking chunks as dirty and notifying block changes) and the game was running pretty well. Each second up to 10.000 blocks were placed at once. Note that for each 10k blocks placed, 100k--300k blocks were removed from the buffer.

I will prepare a PR for discussing the setBlocks method soonish.

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Btw: asdf seems to be a good seed to test a city spawned inside a forest...