chunk_dealloc
chunk_dealloc((void *)arena->spare, chunksize);
chunk_dealloc((void *)chunk, chunksize);
chunk_dealloc((void *)((uintptr_t)ret + chunk_size), alloc_size
chunk_dealloc(ret, alignment - offset);
chunk_dealloc((void *)((uintptr_t)ret + chunk_size),
chunk_dealloc(node->chunk, node->size);
static void chunk_dealloc(void *chunk, size_t size);