Explore a submodule for more performant instances.

[LukaJCB]

As many have said before, stacking multiple monad transformers can be quite inefficient, it'd be cool if we had some kind of story for supporting performant instances for different combination of mtl classes.
Oleg has already done some work in that regard with meow-mtl and at the start of the year, I've also played around with specialized instances at cats-mtl-special.

[iravid]

Happy to contribute https://github.com/iravid/irwst :)

[LukaJCB]

@iravid That looks really cool, I think it'd be a great fit :)