Function is_close_to_chunk 

const fn is_close_to_chunk(
    bb: &BoundingBox,
    chunk_x: i32,
    chunk_z: i32,
    margin: i32,
) -> bool

Check if a bounding box is within margin blocks of a chunk.

Matches vanilla’s StructurePiece.isCloseToChunk(ChunkPos, int).