Make microphysics only loop over levels below some cutoff height

There shouldn't be clouds near the top of the model - and in particular, in the sponge layer. Thus we can gain some efficiency by not performing microphysics calculations on those levels. Also, where pressure and water vapor are very small, microphysics can be subject to roundoff problems (e.g. qv<0) so sometimes it's more robust to skip these calculations.

On the other hand, switching the number of levels we perform our calculations on could screw up our vectorization strategy and maybe our Kokkos loops... so may not be worth it. Also, avoiding artificial cutoff levels seems like a good thing.

SCREAMv1 currently performs microphysics on all vertical levels, while SCREAMv0 has a namelist parameter `trop_cloud_top_lev` specifying the top of the microphysics domain. So long as there truly aren't clouds in these layers, these implementations should be BFB. We should decide, however, if we want to introduce this cutoff in v1.