Run arrays of two-layer model parameters

[chrisroadmap]

Currently openscm-twolayermodel can run arrays of scenarios (of different emissions) given the same two-layer model parameters. This is quick. It would be great to do the opposite - run one emissions scenario with different two-layer parameters, without using a for loop and then appending the results, which is slow. Option could be either to allow runner.du, runner.dl etc be arrays, or allow parameters to be passed in a twolayer-model ScmRun instance along with the emissions to drive the model.

[znicholls]

Given all the parallel infrastructure in https://github.com/openscm/openscm-runner, it might be best to put this functionality there?

[chrisroadmap]

Sure - let's add to that wishlist and close this.