Warn on more than 255 (256?) layers

[kylebarron]

deck picking will stop after 255 layers. Note that each parquet chunk is rendered as one layer. I hit this when testing rendering all of california msft buildings! 11M buildings

[kylebarron]

Probably best to set the max number of chunks per layer to something like 24? However you can't do that from the serialization code because that'll change the number of rows in each batch. Rather you need to do it from the infer_rows_per_chunk call in the BaseArrowLayer

[kylebarron]

Note that this should be 255, not 256, because it needs one element in the channel to say "the picked pixel is not an object at all"