Set a block at world coordinates (clamped to the current chunk).
Read a block at world coordinates within the current chunk (NONE if outside).
Stamp an ASCII template at a world origin. layers[dy][dz] is a row of
chars along +X; each char maps through palette to a block (unmapped chars
— including spaces — are skipped, leaving existing blocks). rot (0–3)
rotates the footprint 90° clockwise about the origin.
Block writer scoped to the chunk being generated; out-of-chunk writes are dropped.