Deduplicate LoopCat and TracedCat about concat HOT 2 OPEN

Cool connection. @lyxia offered section 5.1 of this paper for details on the connection.

DelayCat is necessary to make looping work for streaming-type arrows (Streams, MonadicStreamFunctions, Yampa). The reason is that for a stream to loop it (always?) relies on laziness in the looped value, and on the first iteration, when this undefined recursive variable is forced, what value should it have? It'll be an infinite loop unless you use delay to provide that first value.

As far as names, I tend to aesthetically prefer the Cartesian, Monoidal, etc world of names, because it helps one connect to the CT better, which would suggest Traced is the right choice. But my impression is that this library is tending toward ProductCat etc to use names that are more immediately apparent, which would suggest Loop. I'm not particularly partial between the two options though. The only relevant bike-shedding I'd propose is to move from ProductCat et al to just Product, because if it's already namespaced under Category it's obvious it's a Cat.

from concat.

I'm all for TracedCat. (I like the Cat to be uniform with the type classes that have a non-Cat counterpart such as Functor.)

from concat.