deinit

pub fn deinit(arena: ArenaAllocator) void {
    // NOTE: When changing this, make sure `reset()` is adjusted accordingly!

    for ([_]?*Node{ arena.state.used_list, arena.state.free_list }) |first_node| {
        var it = first_node;
        while (it) |node| {
            // this has to occur before the free because the free frees node
            it = node.next;
            arena.child_allocator.rawFree(node.allocatedSliceUnsafe(), .of(Node), @returnAddress());
        }
    }
}