h3>Ragged Outputs</h3>
<p>The output of each mapped function is concatenated in order of inputs
to produce the output of <code>map_rect</code>. When every shard returns a singleton
(size one) array, the result is the same size as the number of shards
and is easy to deal with downstream. If functions return longer
arrays, they can still be structured using the <code>to_matrix</code>
function if they are rectangular.</p>
<p>If the outputs are of varying sizes, then there will have to be some way
to convert it