Implementation of Better Terrain plugin algorithm using Godot's GDExtension.
Implements get_cell, set_cell(s), update_terrain_area and update_terrain_cell(s), so it can provide fast terrain matching. It is approximately 15x faster than the built-in terrain system, and about 8-10x faster than the Better Terrain plugin. Note that these values are very roughly calculated on my budget laptop. Your mileage may vary.
No support provided; only use this if you know what you're doing.